Table 1 Comparison of P. falciparum and P. vivax passive and active case detection. The study includes individuals followed throughout the year-2003 malaria transmission season (February-July, 2003). Passive case detection was conducted at the Health Post, where individuals presenting with febrile illness are tested for malaria parasites by microscopy. Active case detection was performed in two ways. In March, a community survey was conducted where 957 of the population (N = 1907) were sampled. Then, April-July, sentinel individuals living in houses defined as at-risk zones for P. falciparum transmission were randomly selected. Individuals selected as sentinels were followed prospectively for one month with weekly visits. The passive and "passive and active" (active+passive) prevalence only considers individuals who were enrolled both in the community survey and enrolled as sentinels in at-risk zones for at least one month during these months.
| Â | P. falciparum | P. vivax |
|---|---|---|
Total malaria cases detected by passive case detection February - July, 2003 / total population | 49/1907 = 0.03 | 418/1907 = 0.22 |
No. monthly active case intervals with weekly sampling in at-risk zones (No. of individuals) | 592 (573) | 592 (573) |
Malaria infections detected by active+passive surveillance in at-risk zone sentinels | Total: 74/573 = 0.13 | Total: 224/573 = 0.39 |
Passive case detection, February – July | 15a (20.8%) | 48 (21.4%) |
Community survey, March | 12b (16.7%) | 36b (16.1%) |
Monthly active surveillance in at-risk zones, April – July | 46 (62.5%) | 140 (62.5%) |
Difference in passive versus active+passive prevalence Attributable fraction potentially explained by sampling in at-risk zones and/or asymptomatic infections | 0.13/0.03 = 4.33 | 0.39/0.22 = 1.77 |