Background Asymptomatic Plasmodium falciparum infections are common in Malawi; however, the implications of these infections for the burden of malaria illness are unknown. Whether asymptomatic infections eventually progress to malaria illness, persist without causing symptoms, or clear spontaneously remains undetermined. We identified asymptomatic infections and evaluated the associations between persistent asymptomatic infections and malaria illness. Methods Children and adults (N = 120) who presented at a health facility with uncomplicated malaria were followed monthly for 2 years. During follow-up visits, participants with malaria symptoms were tested and, if positive, treated. Samples from all visits were tested for parasites using both microscopy and polymerase chain reaction, and all malaria infections underwent genotyping. Cox frailty models were used to estimate the temporal association between asymptomatic infections and malaria illness episodes. Mixed models were used to estimate the odds of clinical symptoms associated with new versus persistent infections. Results Participants had a median follow-up time of 720 days. Asymptomatic infections were detected during 23% of visits. Persistent asymptomatic infections were associated with decreased risk of malaria illness in all ages (hazard ratio 0.50, P < .001). When asymptomatic infections preceded malaria illness, newly-acquired infections were detected at 92% of subsequent clinical episodes, independent of presence of persistent infections. Malaria illness among children was more likely due to newly-acquired infections (odds ratio, 1.4; 95% confidence interval, 1.3-1.5) than to persistent infections. Conclusions Asymptomatic P. falciparum infections are associated with decreased incidence of malaria illness, but do not protect against disease when new infection occurs.

中文翻译：

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马拉维无症状恶性疟原虫感染的临床意义。

背景无症状的恶性疟原虫感染在马拉维很常见。但是，这些感染对疟疾负担的影响尚不清楚。无症状感染是否最终发展为疟疾疾病，是否持续而没有引起症状或是否自发清除尚不确定。我们确定了无症状感染，并评估了持续无症状感染与疟疾之间的关联。方法在卫生机构就诊的未患疟疾的儿童和成人（N = 120），每月随访2年。在随访期间，对患有疟疾症状的参与者进行了测试，如果呈阳性，则进行治疗。使用显微镜和聚合酶链反应测试所有来访样本的寄生虫，并对所有疟疾感染进行基因分型。使用Cox脆弱模型估计无症状感染与疟疾发病之间的时间相关性。使用混合模型来估计与新感染和持续感染相关的临床症状的几率。结果参与者的中位随访时间为720天。在23％的就诊过程中检测到无症状感染。在所有年龄段，持续的无症状感染与疟疾患病风险降低相关（危险比0.50，P <.001）。当无症状感染发生在疟疾发病之前时，在随后的临床发作中有92％会检测到新获得的感染，而与持续感染的存在无关。与持续感染相比，儿童中的疟疾疾病更有可能是由于新获得的感染（比值比为1.4； 95％的置信区间为1.3-1.5）。