Branch OraLee, Casapia W Martin, Gamboa Dionicia V, Hernandez Jean N, Alava Freddy F, Roncal Norma, Alvarez Eugenia, Perez Enrique J, Gotuzzo Eduardo
Department of Medicine, Geographic Medicine, University of Alabama at Birmingham, Bevill Research Building BBRB-556, Birmingham 35294-2170, USA.
Malar J. 2005 Jun 23;4:27. doi: 10.1186/1475-2875-4-27.
There is a low incidence of malaria in Iquitos, Peru, suburbs detected by passive case-detection. This low incidence might be attributable to infections clustered in some households/regions and/or undetected asymptomatic infections.
Passive case-detection (PCD) during the malaria season (February-July) and an active case-detection (ACD) community-wide survey (March) surveyed 1,907 persons. Each month, April-July, 100-metre at-risk zones were defined by location of Plasmodium falciparum infections in the previous month. Longitudinal ACD and PCD (ACP+PCD) occurred within at-risk zones, where 137 houses (573 persons) were randomly selected as sentinels, each with one month of weekly active sampling. Entomological captures were conducted in the sentinel houses.
The PCD incidence was 0.03 P. falciparum and 0.22 Plasmodium vivax infections/person/malaria-season. However, the ACD+PCD prevalence was 0.13 and 0.39, respectively. One explanation for this 4.33 and 1.77-fold increase, respectively, was infection clustering within at-risk zones and contiguous households. Clustering makes PCD, generalized to the entire population, artificially low. Another attributable-factor was that only 41% and 24% of the P. falciparum and P. vivax infections were associated with fever and 80% of the asymptomatic infections had low-density or absent parasitaemias the following week. After accounting for asymptomatic infections, a 2.6-fold increase in ACD+PCD versus PCD was attributable to clustered transmission in at-risk zones.
Even in low transmission, there are frequent highly-clustered asymptomatic infections, making PCD an inadequate measure of incidence. These findings support a strategy of concentrating ACD and insecticide campaigns in houses adjacent to houses were malaria was detected one month prior.
通过被动病例检测发现，秘鲁伊基托斯郊区的疟疾发病率较低。这种低发病率可能归因于某些家庭/地区的感染聚集和/或未检测到的无症状感染。
在疟疾季节（2月至7月）进行被动病例检测（PCD），并在3月进行全社区主动病例检测（ACD）调查，共调查了1907人。4月至7月的每个月，根据前一个月恶性疟原虫感染的位置确定100米的风险区域。在风险区域内进行纵向ACD和PCD（ACP+PCD），随机选择137所房屋（573人）作为哨点，每所房屋进行为期一个月的每周主动采样。在哨点房屋进行昆虫捕获。
PCD发病率为每疟疾季节每人0.03例恶性疟原虫感染和0.22例间日疟原虫感染。然而，ACD+PCD患病率分别为0.13和0.39。这种分别增加4.33倍和1.77倍的一个解释是风险区域和相邻家庭内的感染聚集。聚集使得推广到整个人口的PCD人为地偏低。另一个归因因素是，只有41%的恶性疟原虫感染和24%的间日疟原虫感染与发热有关，80%的无症状感染在接下来的一周内寄生虫密度低或无寄生虫血症。在考虑无症状感染后，ACD+PCD相对于PCD增加2.6倍归因于风险区域内的聚集传播。
即使在低传播情况下，也存在频繁的高度聚集的无症状感染，使得PCD不足以作为发病率的衡量指标。这些发现支持将ACD和杀虫剂运动集中在一个月前检测到疟疾的房屋附近房屋的策略。
