葉酸補給とマラリアの抗マラリア薬を摂取している人々の葉酸補給とマラリアの感受性と重症度

背景: 病状の説明 マラリアは、ハマダラカ属の数種のメスの蚊に刺されることによって伝播する感染症で、87 か国で発生しており、伝播が続いています (WHO 2020)。世界保健機関 (WHO) は、2019 年に世界中で約 2 億 2,900 万件のマラリアが発生し、その 94% が WHO のアフリカ地域で発生していると推定しました (WHO 2020)。これらのマラリア症例のうち、世界中で推定 409,000 人が死亡し、その 67% が 5 歳未満の子供で発生しています (WHO 2020)。マラリアは、妊娠、出産、産後の女性の健康にも悪影響を及ぼします (WHO 2020)。葉酸拮抗薬である抗マラリア薬であるスルファドキシン/ピリメタミン（SP）は、1993年にマラウイで初めて導入されて以来、単純型マラリアの第一選択治療としてサハラ以南のアフリカ全土で広く使用されている（Filler 2006）。 SPに対する耐性が増加しているため、2000年にWHOは、熱帯熱マラリア原虫による単純性マラリアの治療には、SPの代わりにアルテミシニンベースの併用療法（ACT）の1つを使用することを推奨した（マラリアをロールバックするための世界パートナーシップ2001）。しかし、これらの推奨にもかかわらず、SP はマラリアの有無にかかわらず、妊娠中の間欠的予防治療 (IPTp) および乳児の間欠的予防治療 (IPTi) を引き続き推奨されています (WHO 2013)。介入の説明 葉酸塩 (ビタミン B9) には、天然に存在する葉酸塩と、栄養補助食品や栄養強化食品に使用されるビタミンの完全酸化モノグルタミン酸形態である葉酸の両方が含まれます。葉酸欠乏症（例、赤血球（RBC）の葉酸濃度が 305 ナノモル/リットル（nmol/L）未満、血清または血漿濃度が 7 nmol/L 未満）は世界の多くの地域で一般的であり、多くの場合巨赤芽球症として現れます。貧血。葉酸の不適切な摂取、必要量の増加、吸収の低下、または葉酸の異常な代謝に起因します（Bailey 2015; WHO 2015a）。妊娠中の女性は葉酸の必要量が多くなります。妊娠1ヶ月前および妊娠1ヶ月中の葉酸摂取量が不十分（赤血球葉酸濃度が400ナノグラム/ミリリットル（ng/mL）または906nmol/L未満で証明される）すると、神経管欠損、早産、低出生体重のリスクが増加します。 、および胎児の発育制限（Bourassa 2019）。 WHO は、妊娠を希望するすべての女性に対し、妊娠を開始してから妊娠 12 週まで毎日 400 マイクログラム (μg) の葉酸を摂取することを推奨しています (WHO 2017)。 2015 年に、WHO は 0.4 mg の葉酸の用量を必須医薬品リストに追加しました (WHO 2015c)。毎日の経口鉄分（30 mg ～ 60 mg の鉄単体）に加えて、神経管欠損、母体貧血、産褥敗血症、低出生体重、および妊婦の貧血が重篤な環境での早産を予防するために、葉酸の補給が妊婦に推奨されます。公衆衛生上の問題（つまり、妊婦の少なくとも 40% の血中ヘモグロビン (Hb) 濃度が 110 g/L 未満である場合）。介入がどのように機能するか 葉酸の状態とマラリア感染との間の潜在的な相互作用 マラリア原虫は生存と成長のために葉酸を必要とします。このことから、葉酸の状態がマラリアのリスクと重症度に影響を与える可能性があるという仮説が生まれました。アカゲザルでは、葉酸が豊富な動物と比較して、葉酸欠乏症はマラリア原虫感染症に対する防御効果があることがわかっています（Metz 2007）。あるいは、マラリアは溶血や発熱による葉酸利用の増加により、葉酸欠乏症を誘発または悪化させる可能性があります。さらに、RBC葉酸塩を介して測定される葉酸塩状態は、マラリア感染者の葉酸塩状態の適切なバイオマーカーではありません。なぜなら、これらの個人のRBC葉酸値は、その人の貯蔵量と寄生虫の葉酸合成の両方を示すからです。ナイジェリアでの研究では、マラリアに感染している子供はマラリアに感染していない子供に比べて赤血球葉酸濃度が有意に高いが、血漿葉酸濃度は同等であることが判明した(Bradley-Moore 1985)。このレビューを行うことが重要な理由 マラリア原虫は、人間の生存と成長のために葉酸を必要とします。個人にとって、適切な葉酸レベルは健康と幸福にとって、また貧血や神経管欠損の予防にとって非常に重要です。多くの国は、リスクにさらされている人々の適切な葉酸状態を確保するために葉酸の補給に依存しています。葉酸サプリメントのさまざまな製剤が多くの国際的な環境で利用可能であり、用量は 400 μg ～ 5 mg の範囲です。サプリメントの取り組みで使用される葉酸の投与量レベルを評価することで、マラリアのリスクと重症度、および治療失敗に対する葉酸の潜在的な影響についての公衆衛生上の理解が深まる可能性があります。葉酸抗葉酸塩抗マラリア薬との相互作用やマラリア疾患の進行との相互作用を調べることは、マラリア流行地域の国が、リスクにさらされている人々に最も適切な低用量の葉酸製剤を決定するのに役立つ可能性がある。 WHOは入手可能な証拠が限られていることを強調し、葉酸塩状態のバイオマーカー、特に赤血球葉酸塩濃度と結核、ヒト免疫不全ウイルス（HIV）、および抗葉酸塩抗マラリア薬との相互作用についてさらなる研究の必要性を示唆した（WHO 2015b）。以前のコクランレビューでは、マラリアの高度風土病地域または蔓延性マラリア地域に住む子供に対する、葉酸の有無にかかわらず鉄補給の効果と安全性を評価しました。発熱や血液中の寄生虫の存在が示すように、鉄補給はマラリアのリスクを増加させないことが実証されました（Neuberger 2016）。さらに、このレビューでは、葉酸がSPの有効性を妨げる可能性があると述べています。ただし、これらの結果に対する葉酸補給の有効性と安全性は確立されていません。このレビューは、マラリア流行地域に住む健康なマラリア感染者に対する毎日の葉酸補給の有効性に関する証拠を提供します。さらに、それは WHO のマラリアに対する世界技術戦略 2016 ～ 2030 (WHO 2015d) と国連の持続可能な開発目標 3 (すべての年齢層の健康な生活を確保し、福祉を促進する) の両方の達成に貢献します (国連) 2021）、異なる用量（例：毎日0.4 mg、1 mg、5 mg）での葉酸補給の潜在的な効果がマラリアの予防または治療に使用される薬剤の効果を妨げるかどうかを評価しています。目的：さまざまな程度のマラリア流行地域に住む人々のマラリア感受性（感染リスク）と重症度に対する、さまざまな用量での葉酸補給の効果を調べること。葉酸サプリメントと葉酸抗マラリア薬との相互作用を調べます。具体的には以下のような回答を目指します。マラリア流行地域に住んでいる非感染者で、マラリア予防のために抗葉酸抗マラリア薬を服用している、または服用していない人々の中で、葉酸含有サプリメントを摂取すると、マラリア感染に対する感受性や重症度が増加しますか?葉酸抗マラリア薬で治療を受けているマラリア感染症患者の場合、葉酸補給により治療失敗のリスクが高まりますか?方法： このレビューの研究を検討するための基準 研究の種類 選択基準 ランダム化比較試験（RCT） マラリア流行地域（撲滅に近づいている地域を含む、マラリアの局所感染が継続している地域）で実施される、個人またはクラスターレベルでのランダム化を伴う準RCT 、世界マラリア報告書 2020 に記載）（WHO 2020） 除外基準 生態学的研究 観察研究 インビボ/インビトロ研究 経済研究 系統的文献レビューおよびメタ分析（関連する系統的文献レビューおよびメタ分析は除外されますが、フラグが付けられます）グレー文献スクリーニング） 参加者の種類 対象基準 マラリア流行地域に居住し、葉酸抗マラリア薬（スルファドキシン/ピリメタミン（SP）、ピリメタミン-ダプソン、ピリメタミン、クロロキン、マラリアの予防または治療のためのプログアニル、コトリモキサゾール）（参加者の70％以上がマラリア流行地域に住んでいる場合、研究が含まれる） ベースライン時に貧血の有無およびマラリア原虫血症の有無を評価する参加者を評価する研究が含まれる基準 マラリアの予防または治療のために葉酸抗マラリア薬を服用していない個人 非マラリア流行地域に住んでいる個人 介入の種類 包含基準 葉酸補給 形態：錠剤、カプセル、分散錠で、任意の用量で、投与中、または定期的に タイミング：投与中葉酸抗マラリア薬の投与前または投与後（4 ～ 6 週間以内） 鉄葉酸補給 介入群と対照群間で同一の同時介入と組み合わせた葉酸補給。共同介入には以下が含まれます： 駆虫治療。マルチビタミンまたは複数の微量栄養素の補給。 5-メチルテトラヒドロ葉酸の補給。除外基準 葉酸塩強化水による葉酸塩 米、小麦、またはトウモロコシの大規模な葉酸強化による葉酸投与 比較対象 プラセボ 治療なし 葉酸なし/異なる用量の葉酸 鉄 アウトカム測定の種類 主要アウトカム 合併症のないマラリア（病歴として定義）寄生虫学的確認を伴う発熱；許容可能な寄生虫学的確認には、迅速診断検査（RDT）、マラリア塗抹標本、または核酸検出（すなわち、ポリメラーゼ連鎖反応（PCR）、ループ媒介等温増幅（LAMP）など）が含まれる）（WHO 2010） ）。この結果は、マラリア予防のために葉酸抗マラリア薬を投与され、マラリアに罹患していない患者に関連する。重症マラリア（重症度の兆候や重要臓器機能不全の証拠、あるいはその両方を伴う脳性マラリアまたは急性熱帯熱マラリアの症例として定義）（WHO 2010）。この結果は、マラリア予防のために葉酸抗マラリア薬を投与され、マラリアに罹患していない患者に関連する。寄生虫除去（任意のプラスモディウム種）。登録時に検査で陽性となった患者が治療を受けて塗抹陰性または PCR 陰性になるまでにかかる時間として定義されます。この結果は、葉酸抗マラリア薬で治療を受けたマラリア患者に当てはまります。治療失敗（臨床症状が解消するかどうかに関係なく、抗マラリア薬投与後にマラリア原虫血症を解消できない、または再燃を防ぐことができないと定義される）（WHO 2019）。この結果は、葉酸抗マラリア薬で治療を受けたマラリア患者に当てはまります。副次的アウトカム 寄生虫血症の期間 寄生虫密度 ヘモグロビン (Hb) 濃度 (g/L) 貧血: 重度の貧血 (妊婦および生後 6 ～ 59 か月の小児の Hb が 70 g/L 未満、および Hb が 80 g/L 未満と定義される)他の集団では）;中等度の貧血（妊婦および生後6～59か月の小児ではHb値が100g/L未満、その他の場合は110g/L未満と定義） 原因を問わず死亡 妊婦の場合：死産（妊娠28週未満） ;低出生体重（2500g未満）。活動性胎盤マラリア（塗抹標本またはPCRによって胎盤血液中に検出されたプラスモジウム、または印象塗抹標本または胎盤の組織学によって検出されたプラスモジウムとして定義される）。研究を特定するための検索方法 日付や言語の制限なく、完了した研究と進行中の研究を特定するために検索が実行されます。電子検索 検索戦略は、関心のある各介入および関心のある研究デザインに関連する適切な主題見出しおよびテキスト単語を含むように設計されます (付録 1 を参照)。検索は、必要に応じて優先順位付けを容易にするために、これら 2 つの基準 (関心のある介入と関心のある研究デザイン) によって分類されます。スコットランド大学間ガイドラインネットワーク (SIGN) が推奨する研究設計フィルターと、MEDLINE および Embase の臨床試験を識別するためにコクランが設計したフィルターが使用されます (SIGN 2020)。日付や言語の制限はありません。含める対象として特定された英語以外の記事は英語に翻訳されます。翻訳が不可能な場合は、コクラン感染症グループにアドバイスが求められ、翻訳が利用可能になるまで記録はレビューの「評価待ち」セクションに保管されます。次の電子データベースで一次研究が検索されます。対照試験のコクラン中央登録簿。看護および関連健康文献の累積インデックス (CINAHL)。エンベース。メドライン。スコーパス。 Web of Science (社会科学引用インデックスと科学引用インデックスの両方)。当社は、関連する進行中または計画中の臨床試験、抄録、およびマラリア流行地域における葉酸補給プログラムに関する評価、研究、調査の全文報告書。さらに、まだ出版されていないが、含める資格がある可能性のある RCT を特定するための灰色文献の手動検索が、以下の情報源で実行されます。グローバルインデックスメディカス（GIM）。アフリカン・インデックス・メディカス（AIM）。東地中海地域のインデックス メディカス (IMEMR)。ラテンアメリカおよびカリブ海健康科学文献 (LILACS)。汎米保健機構 (PAHO)。西太平洋地域インデックス メディカス (WPRO)。東南アジア地域のインデックス メディカス (IMSEAR)。スペイン健康科学書誌索引 (IBECS) (ibecs.isciii.es/)。インド医学研究ジャーナル (IJMR) (journals.lww.com/ijmr/pages/default.aspx)。ネイティブヘルスデータベース (nativehealthdatabase.net/)。シエロ (www.scielo.br/)。他のリソースの検索 過去 12 か月間に含まれた研究数が最も多かった 5 つのジャーナルを手作業で検索し、検索時にデータベースに索引付けされていない可能性のある関連論文を収集します。私たちは、含まれている研究の著者に連絡し、追加の記録を特定するために含まれている論文の参考文献リストを確認します。進行中の研究または未発表の研究を特定する際の支援が必要な場合は、CDC、国連世界食糧計画 (WFP) の栄養・身体活動・肥満部門 (DNPAO) および寄生虫病・マラリア部門 (DPDM) に連絡します。ニュートリション・インターナショナル（NI）、栄養改善のためのグローバル・アライアンス（GAIN）、ヘレン・ケラー・インターナショナル（HKI）。データの収集と分析 研究の選択 2 人のレビュー著者が、各検索で取得された論文のタイトルと要約を独立してスクリーニングし、包含基準と除外基準によって決定される適格性を評価します。抄録審査段階で両方の査読者によって掲載に適格であるとみなされた研究は全文審査段階に進み、適格なすべての論文の全文コピーが取得されます。論文全文を入手できない場合は、研究のさらなる詳細を得るために著者に連絡を試みます。そのような情報が得られない場合、さらなる情報が公開されるか利用可能になるまで、その研究は「評価待ち」として分類されます。同じ 2 人のレビュー著者が、体系的レビューに含めるための全文論文の適格性を独立して評価します。 2 人のレビュー著者が選択した研究間に矛盾が生じた場合、3 人目のレビュー著者が仲裁を行います。各試験は精査され、同じデータセットから複数の出版物が特定され、除外された試験の正当性が文書化されます。研究選択プロセスの PRISMA フロー図は、文献検索で特定された記録の数、含まれる研究と除外される研究の数、および除外の理由に関する情報を提供するために提示されます (Moher 2009)。除外された研究のリストと、全文スクリーニング段階での除外理由も作成されます。データの抽出と管理 2 人のレビュー著者が、標準化されたデータ仕様フォームを使用して、含まれる研究の最終リストのデータを個別に抽出します。 2 人の著者によって抽出されたデータ間に観察された不一致は、3 人目のレビュー著者が参加して合意に達することで解決されます。研究デザインの構成要素、ベースラインの参加者の特性、介入の特性、および結果に関する情報が抽出されます。個別にランダム化された試験の場合、イベントを経験した参加者の数と各治療グループで分析された数、または二分法結果尺度について報告された効果推定値（リスク比（RR）など）を記録します。カウントデータとして、各グループのイベント数と追跡の人月数を記録します。人月数が報告されない場合は、追跡期間と評価された子供の数の積を使用してこの数値を推定します。各研究の速度比と標準誤差 (SE) を計算します。ゼロ イベントは 0.5 に置き換えられます。元の研究で報告されている場合は、調整済みと未調整の両方の共変量発生率比を抽出します。連続データの場合、平均 (算術または幾何) と分散の尺度 (標準偏差 (SD)、SE、または信頼区間 (CI))、ベースラインからのパーセンテージまたは平均変化、および各グループで分析された数値を抽出します。 SD は、値の正規分布を仮定して、SE または 95% CI から計算されます。 g/dL 単位のヘモグロビン値は、ヘマトクリットまたは充填細胞容積の値に 0.34 を乗算して計算され、g/dL 単位でヘモグロビン値を報告する研究は g/L に変換されます。クラスターランダム化試験では、ランダム化の単位 (世帯、複合施設、部門、村など)、試験内のクラスターの数、および平均クラスターサイズを記録します。試験の分析に使用された統計的手法は、これらの手法がクラスタリングまたは他の共変量に対して調整されたかどうかを説明する詳細とともに文書化されます。各結果のクラスター内相関係数 (ICC) の推定値を抽出する予定です。結果がクラスタリング用に調整される場合、治療効果の推定値と SD または CI を抽出します。結果がクラスタリング用に調整されていない場合は、報告されたデータが抽出されます。含まれた研究におけるバイアスのリスクの評価 2 人のレビュー著者 (KSC、LFY) は、ランダム化研究に対してコクランの「バイアスのリスク 2」ツール (RoB 2) を使用して、含まれた各試験のバイアスのリスクを独立して評価します (Sterne 2019)。含まれる研究のバイアスのリスクに関する判断は、介入の系統的レビューのためのコクランハンドブック (Higgins 2021) に概説されている推奨事項に従って行われます。意見の相違は、議論するか、第 3 のレビュー著者を参加させることによって解決されます。私たちのレビューの目的は、ベースラインでの介入への割り当ての効果を評価することです。 RoB2 ツールを使用して各主要結果を評価します。 Cochrane RoB2 ツールの 5 つのドメインには次のものが含まれます。ランダム化プロセスから生じるバイアス。意図した介入からの逸脱によるバイアス。結果データの欠落によるバイアス。結果の測定におけるバイアス。報告された結果の選択におけるバイアス。 RoB2 ツールの各ドメインは以下で構成されます。一連の「シグナル」質問。ドメインのバイアスのリスクに関する判断。シグナリング質問に対する回答を提案された判断にマッピングするアルゴリズムによって促進されます。シグナルとなる質問や「偏見のリスク」の判断に対する回答を正当化するためのフリーテキストボックス。バイアスの可能性のある方向を予測 (および説明) するオプション。信号を送る質問への応答により、関連する情報が導き出されます

BACKGROUND: Description of the condition Malaria, an infectious disease transmitted by the bite of female mosquitoes from several Anopheles species, occurs in 87 countries with ongoing transmission (WHO 2020). The World Health Organization (WHO) estimated that, in 2019, approximately 229 million cases of malaria occurred worldwide, with 94% occurring in the WHO's African region (WHO 2020). Of these malaria cases, an estimated 409,000 deaths occurred globally, with 67% occurring in children under five years of age (WHO 2020). Malaria also negatively impacts the health of women during pregnancy, childbirth, and the postnatal period (WHO 2020). Sulfadoxine/pyrimethamine (SP), an antifolate antimalarial, has been widely used across sub-Saharan Africa as the first-line treatment for uncomplicated malaria since it was first introduced in Malawi in 1993 (Filler 2006). Due to increasing resistance to SP, in 2000 the WHO recommended that one of several artemisinin-based combination therapies (ACTs) be used instead of SP for the treatment of uncomplicated malaria caused by Plasmodium falciparum (Global Partnership to Roll Back Malaria 2001). However, despite these recommendations, SP continues to be advised for intermittent preventive treatment in pregnancy (IPTp) and intermittent preventive treatment in infants (IPTi), whether the person has malaria or not (WHO 2013). Description of the intervention Folate (vitamin B9) includes both naturally occurring folates and folic acid, the fully oxidized monoglutamic form of the vitamin, used in dietary supplements and fortified food. Folate deficiency (e.g. red blood cell (RBC) folate concentrations of less than 305 nanomoles per litre (nmol/L); serum or plasma concentrations of less than 7 nmol/L) is common in many parts of the world and often presents as megaloblastic anaemia, resulting from inadequate intake, increased requirements, reduced absorption, or abnormal metabolism of folate (Bailey 2015; WHO 2015a). Pregnant women have greater folate requirements; inadequate folate intake (evidenced by RBC folate concentrations of less than 400 nanograms per millilitre (ng/mL), or 906 nmol/L) prior to and during the first month of pregnancy increases the risk of neural tube defects, preterm delivery, low birthweight, and fetal growth restriction (Bourassa 2019). The WHO recommends that all women who are trying to conceive consume 400 micrograms (µg) of folic acid daily from the time they begin trying to conceive through to 12 weeks of gestation (WHO 2017). In 2015, the WHO added the dosage of 0.4 mg of folic acid to the essential drug list (WHO 2015c). Alongside daily oral iron (30 mg to 60 mg elemental iron), folic acid supplementation is recommended for pregnant women to prevent neural tube defects, maternal anaemia, puerperal sepsis, low birthweight, and preterm birth in settings where anaemia in pregnant women is a severe public health problem (i.e. where at least 40% of pregnant women have a blood haemoglobin (Hb) concentration of less than 110 g/L). How the intervention might work Potential interactions between folate status and malaria infection The malaria parasite requires folate for survival and growth; this has led to the hypothesis that folate status may influence malaria risk and severity. In rhesus monkeys, folate deficiency has been found to be protective against Plasmodium cynomolgi malaria infection, compared to folate-replete animals (Metz 2007). Alternatively, malaria may induce or exacerbate folate deficiency due to increased folate utilization from haemolysis and fever. Further, folate status measured via RBC folate is not an appropriate biomarker of folate status in malaria-infected individuals since RBC folate values in these individuals are indicative of both the person's stores and the parasite's folate synthesis. A study in Nigeria found that children with malaria infection had significantly higher RBC folate concentrations compared to children without malaria infection, but plasma folate levels were similar (Bradley-Moore 1985). Why it is important to do this review The malaria parasite needs folate for survival and growth in humans. For individuals, adequate folate levels are critical for health and well-being, and for the prevention of anaemia and neural tube defects. Many countries rely on folic acid supplementation to ensure adequate folate status in at-risk populations. Different formulations for folic acid supplements are available in many international settings, with dosages ranging from 400 µg to 5 mg. Evaluating folic acid dosage levels used in supplementation efforts may increase public health understanding of its potential impacts on malaria risk and severity and on treatment failures. Examining folic acid interactions with antifolate antimalarial medications and with malaria disease progression may help countries in malaria-endemic areas determine what are the most appropriate lower dose folic acid formulations for at-risk populations. The WHO has highlighted the limited evidence available and has indicated the need for further research on biomarkers of folate status, particularly interactions between RBC folate concentrations and tuberculosis, human immunodeficiency virus (HIV), and antifolate antimalarial drugs (WHO 2015b). An earlier Cochrane Review assessed the effects and safety of iron supplementation, with or without folic acid, in children living in hyperendemic or holoendemic malaria areas; it demonstrated that iron supplementation did not increase the risk of malaria, as indicated by fever and the presence of parasites in the blood (Neuberger 2016). Further, this review stated that folic acid may interfere with the efficacy of SP; however, the efficacy and safety of folic acid supplementation on these outcomes has not been established. This review will provide evidence on the effectiveness of daily folic acid supplementation in healthy and malaria-infected individuals living in malaria-endemic areas. Additionally, it will contribute to achieving both the WHO Global Technical Strategy for Malaria 2016-2030 (WHO 2015d), and United Nations Sustainable Development Goal 3 (to ensure healthy lives and to promote well-being for all of all ages) (United Nations 2021), and evaluating whether the potential effects of folic acid supplementation, at different doses (e.g. 0.4 mg, 1 mg, 5 mg daily), interferes with the effect of drugs used for prevention or treatment of malaria. OBJECTIVES: To examine the effects of folic acid supplementation, at various doses, on malaria susceptibility (risk of infection) and severity among people living in areas with various degrees of malaria endemicity. We will examine the interaction between folic acid supplements and antifolate antimalarial drugs. Specifically, we will aim to answer the following. Among uninfected people living in malaria endemic areas, who are taking or not taking antifolate antimalarials for malaria prophylaxis, does taking a folic acid-containing supplement increase susceptibility to or severity of malaria infection? Among people with malaria infection who are being treated with antifolate antimalarials, does folic acid supplementation increase the risk of treatment failure? METHODS: Criteria for considering studies for this review Types of studies Inclusion criteria Randomized controlled trials (RCTs) Quasi-RCTs with randomization at the individual or cluster level conducted in malaria-endemic areas (areas with ongoing, local malaria transmission, including areas approaching elimination, as listed in the World Malaria Report 2020) (WHO 2020) Exclusion criteria Ecological studies Observational studies In vivo/in vitro studies Economic studies Systematic literature reviews and meta-analyses (relevant systematic literature reviews and meta-analyses will be excluded but flagged for grey literature screening) Types of participants Inclusion criteria Individuals of any age or gender, living in a malaria endemic area, who are taking antifolate antimalarial medications (including but not limited to sulfadoxine/pyrimethamine (SP), pyrimethamine-dapsone, pyrimethamine, chloroquine and proguanil, cotrimoxazole) for the prevention or treatment of malaria (studies will be included if more than 70% of the participants live in malaria-endemic regions) Studies assessing participants with or without anaemia and with or without malaria parasitaemia at baseline will be included Exclusion criteria Individuals not taking antifolate antimalarial medications for prevention or treatment of malaria Individuals living in non-malaria endemic areas Types of interventions Inclusion criteria Folic acid supplementation Form: in tablet, capsule, dispersible tablet at any dose, during administration, or periodically Timing: during, before, or after (within a period of four to six weeks) administration of antifolate antimalarials Iron-folic acid supplementation Folic acid supplementation in combination with co-interventions that are identical between the intervention and control groups. Co-interventions include: anthelminthic treatment; multivitamin or multiple micronutrient supplementation; 5-methyltetrahydrofolate supplementation. Exclusion criteria Folate through folate-fortified water Folic acid administered through large-scale fortification of rice, wheat, or maize Comparators Placebo No treatment No folic acid/different doses of folic acid Iron Types of outcome measures Primary outcomes Uncomplicated malaria (defined as a history of fever with parasitological confirmation; acceptable parasitological confirmation will include rapid diagnostic tests (RDTs), malaria smears, or nucleic acid detection (i.e. polymerase chain reaction (PCR), loop-mediated isothermal amplification (LAMP), etc.)) (WHO 2010). This outcome is relevant for patients without malaria, given antifolate antimalarials for malaria prophylaxis. Severe malaria (defined as any case with cerebral malaria or acute P. falciparum malaria, with signs of severity or evidence of vital organ dysfunction, or both) (WHO 2010). This outcome is relevant for patients without malaria, given antifolate antimalarials for malaria prophylaxis. Parasite clearance (any Plasmodium species), defined as the time it takes for a patient who tests positive at enrolment and is treated to become smear-negative or PCR negative. This outcome is relevant for patients with malaria, treated with antifolate antimalarials. Treatment failure (defined as the inability to clear malaria parasitaemia or prevent recrudescence after administration of antimalarial medicine, regardless of whether clinical symptoms are resolved) (WHO 2019). This outcome is relevant for patients with malaria, treated with antifolate antimalarials. Secondary outcomes Duration of parasitaemia Parasite density Haemoglobin (Hb) concentrations (g/L) Anaemia: severe anaemia (defined as Hb less than 70 g/L in pregnant women and children aged six to 59 months; and Hb less than 80 g/L in other populations); moderate anaemia (defined as Hb less than 100 g/L in pregnant women and children aged six to 59 months; and less than 110 g/L in others) Death from any cause Among pregnant women: stillbirth (at less than 28 weeks gestation); low birthweight (less than 2500 g); active placental malaria (defined as Plasmodium detected in placental blood by smear or PCR, or by Plasmodium detected on impression smear or placental histology). Search methods for identification of studies A search will be conducted to identify completed and ongoing studies, without date or language restrictions. Electronic searches A search strategy will be designed to include the appropriate subject headings and text word terms related to each intervention of interest and study design of interest (see Appendix 1). Searches will be broken down by these two criteria (intervention of interest and study design of interest) to allow for ease of prioritization, if necessary. The study design filters recommended by the Scottish Intercollegiate Guidelines Network (SIGN), and those designed by Cochrane for identifying clinical trials for MEDLINE and Embase, will be used (SIGN 2020). There will be no date or language restrictions. Non-English articles identified for inclusion will be translated into English. If translations are not possible, advice will be requested from the Cochrane Infectious Diseases Group and the record will be stored in the "Awaiting assessment" section of the review until a translation is available. The following electronic databases will be searched for primary studies. Cochrane Central Register of Controlled Trials. Cumulative Index to Nursing and Allied Health Literature (CINAHL). Embase. MEDLINE. Scopus. Web of Science (both the Social Science Citation Index and the Science Citation Index). We will conduct manual searches of ClinicalTrials.gov, the International Clinical Trials Registry Platform (ICTRP), and the United Nations Children's Fund (UNICEF) Evaluation and Research Database (ERD), in order to identify relevant ongoing or planned trials, abstracts, and full-text reports of evaluations, studies, and surveys related to programmes on folic acid supplementation in malaria-endemic areas. Additionally, manual searches of grey literature to identify RCTs that have not yet been published but are potentially eligible for inclusion will be conducted in the following sources. Global Index Medicus (GIM). African Index Medicus (AIM). Index Medicus for the Eastern Mediterranean Region (IMEMR). Latin American & Caribbean Health Sciences Literature (LILACS). Pan American Health Organization (PAHO). Western Pacific Region Index Medicus (WPRO). Index Medicus for the South-East Asian Region (IMSEAR). The Spanish Bibliographic Index in Health Sciences (IBECS) (ibecs.isciii.es/). Indian Journal of Medical Research (IJMR) (journals.lww.com/ijmr/pages/default.aspx). Native Health Database (nativehealthdatabase.net/). Scielo (www.scielo.br/). Searching other resources Handsearches of the five journals with the highest number of included studies in the last 12 months will be conducted to capture any relevant articles that may not have been indexed in the databases at the time of the search. We will contact the authors of included studies and will check reference lists of included papers for the identification of additional records. For assistance in identifying ongoing or unpublished studies, we will contact the Division of Nutrition, Physical Activity, and Obesity (DNPAO) and the Division of Parasitic Diseases and Malaria (DPDM) of the CDC, the United Nations World Food Programme (WFP), Nutrition International (NI), Global Alliance for Improved Nutrition (GAIN), and Hellen Keller International (HKI). Data collection and analysis Selection of studies Two review authors will independently screen the titles and abstracts of articles retrieved by each search to assess eligibility, as determined by the inclusion and exclusion criteria. Studies deemed eligible for inclusion by both review authors in the abstract screening phase will advance to the full-text screening phase, and full-text copies of all eligible papers will be retrieved. If full articles cannot be obtained, we will attempt to contact the authors to obtain further details of the studies. If such information is not obtained, we will classify the study as "awaiting assessment" until further information is published or made available to us. The same two review authors will independently assess the eligibility of full-text articles for inclusion in the systematic review. If any discrepancies occur between the studies selected by the two review authors, a third review author will provide arbitration. Each trial will be scrutinized to identify multiple publications from the same data set, and the justification for excluded trials will be documented. A PRISMA flow diagram of the study selection process will be presented to provide information on the number of records identified in the literature searches, the number of studies included and excluded, and the reasons for exclusion (Moher 2009). The list of excluded studies, along with their reasons for exclusion at the full-text screening phase, will also be created. Data extraction and management Two review authors will independently extract data for the final list of included studies using a standardized data specification form. Discrepancies observed between the data extracted by the two authors will be resolved by involving a third review author and reaching a consensus. Information will be extracted on study design components, baseline participant characteristics, intervention characteristics, and outcomes. For individually randomized trials, we will record the number of participants experiencing the event and the number analyzed in each treatment group or the effect estimate reported (e.g. risk ratio (RR)) for dichotomous outcome measures. For count data, we will record the number of events and the number of person-months of follow-up in each group. If the number of person-months is not reported, the product of the duration of follow-up and the number of children evaluated will be used to estimate this figure. We will calculate the rate ratio and standard error (SE) for each study. Zero events will be replaced by 0.5. We will extract both adjusted and unadjusted covariate incidence rate ratios if they are reported in the original studies. For continuous data, we will extract means (arithmetic or geometric) and a measure of variance (standard deviation (SD), SE, or confidence interval (CI)), percentage or mean change from baseline, and the numbers analyzed in each group. SDs will be computed from SEs or 95% CIs, assuming a normal distribution of the values. Haemoglobin values in g/dL will be calculated by multiplying haematocrit or packed cell volume values by 0.34, and studies reporting haemoglobin values in g/dL will be converted to g/L. In cluster-randomized trials, we will record the unit of randomization (e.g. household, compound, sector, or village), the number of clusters in the trial, and the average cluster size. The statistical methods used to analyze the trials will be documented, along with details describing whether these methods adjusted for clustering or other covariates. We plan to extract estimates of the intra-cluster correlation coefficient (ICC) for each outcome. Where results are adjusted for clustering, we will extract the treatment effect estimate and the SD or CI. If the results are not adjusted for clustering, we will extract the data reported. Assessment of risk of bias in included studies Two review authors (KSC, LFY) will independently assess the risk of bias for each included trial using the Cochrane 'Risk of bias 2' tool (RoB 2) for randomized studies (Sterne 2019). Judgements about the risk of bias of included studies will be made according to the recommendations outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2021). Disagreements will be resolved by discussion, or by involving a third review author. The interest of our review will be to assess the effect of assignment to the interventions at baseline. We will evaluate each primary outcome using the RoB2 tool. The five domains of the Cochrane RoB2 tool include the following. Bias arising from the randomization process. Bias due to deviations from intended interventions. Bias due to missing outcome data. Bias in measurement of the outcome. Bias in selection of the reported result. Each domain of the RoB2 tool comprises the following. A series of 'signalling' questions. A judgement about the risk of bias for the domain, facilitated by an algorithm that maps responses to the signalling questions to a proposed judgement. Free-text boxes to justify responses to the signalling questions and 'Risk of bias' judgements. An option to predict (and explain) the likely direction of bias. Responses to signalling questions elicit information relevant to an assessment of the risk of bias. These response options are as follows. Yes (may indicate either low or high risk of bias, depending on the most natural way to ask the question). Probably yes. Probably no. No. No information (may indicate no evidence of that problem or an absence of information leading to concerns about there being a problem). Based on the answer to the signalling question, a 'Risk of bias' judgement is assigned to each domain. These judgements include one of the following. High risk of bias Low risk of bias Some concerns To generate the risk of bias judgement for each domain in the randomized studies, we will use the Excel template, available at www.riskofbias.info/welcome/rob-2-0-tool/current-version-of-rob-2. This file will be stored on a scientific data website, available to readers. Risk of bias in cluster randomized controlled trials For the cluster randomized trials, we will be using the RoB2 tool to analyze the five standard domains listed above along with Domain 1b (bias arising from the timing of identification or recruitment of participants) and its related signalling questions. To generate the risk of bias judgement for each domain in the cluster RCTs, we will use the Excel template available at https://sites.google.com/site/riskofbiastool/welcome/rob-2-0-tool/rob-2-for-cluster-randomized-trials. This file will be stored on a scientific data website, available to readers. Risk of bias in cross-over randomized controlled trials For cross-over randomized trials, we will be using the RoB2 tool to analyze the five standard domains listed above along with Domain 2 (bias due to deviations from intended interventions), and Domain 3 (bias due to missing outcome data), and their respective signalling questions. To generate the risk of bias judgement for each domain in the cross-over RCTs, we will use the Excel template, available at https://sites.google.com/site/riskofbiastool/welcome/rob-2-0-tool/rob-2-for-crossover-trials, for each risk of bias judgement of cross-over randomized studies. This file will be stored on a scientific data website, available to readers. Overall risk of bias The overall 'Risk of bias' judgement for each specific trial being assessed will be based on each domain-level judgement. The overall judgements include the following. Low risk of bias (the trial is judged to be at low risk of bias for all domains). Some concerns (the trial is judged to raise some concerns in at least one domain but is not judged to be at high risk of bias for any domain). High risk of bias (the trial is judged to be at high risk of bias in at least one domain, or is judged to have some concerns for multiple domains in a way that substantially lowers confidence in the result). The 'risk of bias' assessments will inform our GRADE evaluations of the certainty of evidence for our primary outcomes presented in the 'Summary of findings' tables and will also be used to inform the sensitivity analyses; (see Sensitivity analysis). If there is insufficient information in study reports to enable an assessment of the risk of bias, studies will be classified as "awaiting assessment" until further information is published or made available to us. Measures of treatment effect Dichotomous data For dichotomous data, we will present proportions and, for two-group comparisons, results as average RR or odds ratio (OR) with 95% CIs. Ordered categorical data Continuous data We will report results for continuous outcomes as the mean difference (MD) with 95% CIs, if outcomes are measured in the same way between trials. Where some studies have reported endpoint data and others have reported change-from-baseline data (with errors), we will combine these in the meta-analysis, if the outcomes were reported using the same scale. We will use the standardized mean difference (SMD), with 95% CIs, to combine trials that measured the same outcome but used different methods. If we do not find three or more studies for a pooled analysis, we will summarize the results in a narrative form. Unit of analysis issues Cluster-randomized trials We plan to combine results from both cluster-randomized and individually randomized studies, providing there is little heterogeneity between the studies. If the authors of cluster-randomized trials conducted their analyses at a different level from that of allocation, and they have not appropriately accounted for the cluster design in their analyses, we will calculate the trials' effective sample sizes to account for the effect of clustering in data. When one or more cluster-RCT reports RRs adjusted for clustering, we will compute cluster-adjusted SEs for the other trials. When none of the cluster-RCTs provide cluster-adjusted RRs, we will adjust the sample size for clustering. We will divide, by the estimated design effects (DE), the number of events and number evaluated for dichotomous outcomes and the number evaluated for continuous outcomes, where DE = 1 + ((average cluster size 1) * ICC). The derivation of the estimated ICCs and DEs will be reported. We will utilize the intra-cluster correlation coefficient (ICC), derived from the trial (if available), or from another source (e.g., using the ICCs derived from other, similar trials) and then calculate the design effect with the formula provided in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2021). If this approach is used, we will report it and undertake sensitivity analysis to investigate the effect of variations in ICC. Studies with more than two treatment groups If we identify studies with more than two intervention groups (multi-arm studies), where possible we will combine groups to create a single pair-wise comparison or use the methods set out in the Cochrane Handbook to avoid double counting study participants (Higgins 2021). For the subgroup analyses, when the control group was shared by two or more study arms, we will divide the control group (events and total population) over the number of relevant subgroups to avoid double counting the participants. Trials with several study arms can be included more than once for different comparisons. Cross-over trials From cross-over trials, we will consider the first period of measurement only and will analyze the results together with parallel-group studies. Multiple outcome events In several outcomes, a participant might experience more than one outcome event during the trial period. For all outcomes, we will extract the number of participants with at least one event. Dealing with missing data We will contact the trial authors if the available data are unclear, missing, or reported in a format that is different from the format needed. We aim to perform a 'per protocol' or 'as observed' analysis; otherwise, we will perform a complete case analysis. This means that for treatment failure, we will base the analyses on the participants who received treatment and the number of participants for which there was an inability to clear malarial parasitaemia or prevent recrudescence after administration of an antimalarial medicine reported in the studies. Assessment of heterogeneity Heterogeneity in the results of the trials will be assessed by visually examining the forest plot to detect non-overlapping CIs, using the Chi2 test of heterogeneity (where a P value of less than 0.1 indicates statistical significance) and the I2 statistic of inconsistency (with a value of greater than 50% denoting moderate levels of heterogeneity). When statistical heterogeneity is present, we will investigate the reasons for it, using subgroup analysis. Assessment of reporting biases We will construct a funnel plot to assess the effect of small studies for the main outcome (when including more than 10 trials). Data synthesis The primary analysis will include all eligible studies that provide data regardless of the overall risk of bias as assessed by the RoB2 tool. Analyses will be conducted using Review Manager 5.4 (Review Manager 2020). Cluster-RCTs will be included in the main analysis after adjustment for clustering (see the previous section on cluster-RCTs). The meta-analysis will be performed using the Mantel-Haenszel random-effects model or the generic inverse variance method (when adjustment for clustering is performed by adjusting SEs), as appropriate. Subgroup analysis and investigation of heterogeneity The overall risk of bias will not be used as the basis in conducting our subgroup analyses. However, where data are available, we plan to conduct the following subgroup analyses, independent of heterogeneity. Dose of folic acid supplementation: higher doses (4 mg or more, daily) versus lower doses (less than 4 mg, daily). Moderate-severe anaemia at baseline (mean haemoglobin of participants in a trial at baseline below 100 g/L for pregnant women and children aged six to 59 months, and below 110 g/L for other populations) versus normal at baseline (mean haemoglobin above 100 g/L for pregnant women and children aged six to 59 months, and above 110 g/L for other populations). Antimalarial drug resistance to parasite: known resistance versus no resistance versus unknown/mixed/unreported parasite resistance. Folate status at baseline: Deficient (e.g. RBC folate concentration of less than 305 nmol/L, or serum folate concentration of less than 7nmol/L) and Insufficient (e.g. RBC folate concentration from 305 to less than 906 nmol/L, or serum folate concentration from 7 to less than 25 nmol/L) versus Sufficient (e.g. RBC folate concentration above 906 nmol/L, or serum folate concentration above 25 nmol/L). Presence of anaemia at baseline: yes versus no. Mandatory fortification status: yes, versus no (voluntary or none). We will only use the primary outcomes in any subgroup analyses, and we will limit subgroup analyses to those outcomes for which three or more trials contributed data. Comparisons between subgroups will be performed using Review Manager 5.4 (Review Manager 2020). Sensitivity analysis We will perform a sensitivity analysis, using the risk of bias as a variable to explore the robustness of the findings in our primary outcomes. We will verify the behaviour of our estimators by adding and removing studies with a high risk of bias overall from the analysis. That is, studies with a low risk of bias versus studies with a high risk of bias. Summary of findings and assessment of the certainty of the evidence For the assessment across studies, we will use the GRADE approach, as outlined in (Schünemann 2021). We will use the five GRADE considerations (study limitations based on RoB2 judgements, consistency of effect, imprecision, indirectness, and publication bias) to assess the certainty of the body of evidence as it relates to the studies which contribute data to the meta-analyses for the primary outcomes. The GRADEpro Guideline Development Tool (GRADEpro) will be used to import data from Review Manager 5.4 (Review Manager 2020) to create 'Summary of Findings' tables. The primary outcomes for the main comparison will be listed with estimates of relative effects, along with the number of participants and studies contributing data for those outcomes. These tables will provide outcome-specific information concerning the overall certainty of evidence from studies included in the comparison, the magnitude of the effect of the interventions examined, and the sum of available data on the outcomes we considered. We will include only primary outcomes in the summary of findings tables. For each individual outcome, two review authors (KSC, LFY) will independently assess the certainty of the evidence using the GRADE approach (Balshem 2011). For assessments of the overall certainty of evidence for each outcome that includes pooled data from included trials, we will downgrade the evidence from 'high certainty' by one level for serious (or by two for very serious) study limitations (risk of bias, indirectness of evidence, serious inconsistency, imprecision of effect estimates, or potential publication bias).