A community-based study of factors associated with continuing transmission of lymphatic filariasis in Leogane, Haiti

Abstract

Seven rounds of mass drug administration (MDA) have been administered in Leogane, Haiti, an area hyperendemic for lymphatic filariasis (LF). Sentinel site surveys showed that the prevalence of microfilaremia was reduced to <1% from levels as high as 15.5%, suggesting that transmission had been reduced. A separate 30-cluster survey of 2- to 4-year-old children was conducted to determine if MDA interrupted transmission. Antigen and antifilarial antibody prevalence were 14.3% and 19.7%, respectively. Follow-up surveys were done in 6 villages, including those selected for the cluster survey, to assess risk factors related to continued LF transmission and to pinpoint hotspots of transmission. One hundred houses were mapped in each village using GPS-enabled PDAs, and then 30 houses and 10 alternates were chosen for testing. All individuals in selected houses were asked to participate in a short survey about participation in MDA, history of residence in Leogane and general knowledge of LF. Survey teams returned to the houses at night to collect blood for antigen testing, microfilaremia and Bm14 antibody testing and collected mosquitoes from these communities in parallel. Antigen prevalence was highly variable among the 6 villages, with the highest being 38.2% (Dampus) and the lowest being 2.9% (Corail Lemaire); overall antigen prevalence was 18.5%. Initial cluster surveys of 2- to 4-year-old children were not related to community antigen prevalence. Nearest neighbor analysis found evidence of clustering of infection suggesting that LF infection was focal in distribution. Antigen prevalence among individuals who were systematically noncompliant with the MDAs, i.e. they had never participated, was significantly higher than among compliant individuals (p<0.05). A logistic regression model found that of the factors examined for association with infection, only noncompliance was significantly associated with infection. Thus, continuing transmission of LF seems to be linked to rates of systematic noncompliance.

Figure 1. Age prevalence curves based on the various infection measures.

Data are summarized across all communities. MF = microfilaremia ICT = filarial antigen detected by ICT card test. Og4C3  =  ELISA assay to detect filarial antigen Bm14 =  filarial antibody ELISA.

Figure 2. Prevalence of systematic noncompliant individuals by community.

Individuals were considered noncompliant if they had reported never participating in MDA (i.e. systematic noncompliance).

Figure 3. Prevalence of infection in compliant and noncompliant persons by community.

ICT card test was used to determine infection prevalence. Noncompliant individuals were those who reported never participating in MDA. Compliant individuals were those who reported ever haven taken a drug for LF. The asterisk indicates a p-value <0.05. by Chi-square test.