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Lymphatic filariasis is estimated to affect approximately 120 million people in 80 endemic countries worldwide. In Sri Lanka, lymphatic filariasis remains a public health problem, but the real burden of disease remains unknown. This study examines the correlation between varying rates of transmission and theoccurrence of clinical disease, among the residents of the Colombo District. The aggregation of infection at household level was also examined. A cross sectional survey was conducted from January 2001 to December 2002 to assess the prevalence of clinical disease and transmission indices in the Colombo District. A total of 3766 individuals participated in the study, with ages ranging from 10 - 92 years (mean 36.4 years); 54.8 precent were females. The overall prevalence of microfilaraemia and antigenaemia was 0.6 precent and 12.6 precent respectively. A higher prevalence of microfilaraemia was observed among males (1.1 precent) when compared to females (0.2 precent). Prevalence ofantigenaemia was significantly higher in males than infemales (15.8 precent vs 9.9 precent, 'l = 28.7, P\<0.005) and highest in the 30 - 39 year age group. All microfilaraemic persons were antigen-positive. Vector density varied from 10.2 to 33.5 man-hour catch within the study area. The highest Transmission Intensity Index observed was 0.25. Nocturnal cough of over two weeks duration was the most common clinical manifestation encountered. Males were more likely to be affected than females (6.3 precent vs 3.5 precent, odds ratio 1.9 [95 precent CI: 1.4 - 2.4]). The 30-39 year age group was the most severely affected. Hydrocoele affected 0.8 precent of the males in the study population. The prevalence of hydrocoele increased with age, with 1.0 precent of the 50-59 year age group showing this disease manifestation. Attacks of adenolymphangitis and lymphadenitis associated with fever were rare. Lymphoedema of the limbs was also uncommon, affecting only 0.3 precent of males and 0.4 precent of females. The highest age-specific prevalence oflymphoedema of 1.0 precent was observed in the 50-59 year age group. Elephantiasis was seen only in 3 individuals aged over 50 years. All 23 microfilaraemic individuals were asymptomatic; the prevalence of microfilaraemia among individuals with clinical features of lymphatic filariasis was O.However, the prevalence of antigenaemia among those with nocturnal cough suggestive ofTPE was 47.8 precent and 42.8 precent men with hydrocoele were also antigenaemic. The presence of antigenaemia was associated with a statistically significant relative risk of 6.4 (95 precent CI 4.8 - 8.4) for nocturnal cough suggestive of TPE, and a relative risk of 4.0 (95 precent CI 1.4 - 11.5) for hydrocoele. There was no significant association between antigenaemia and ADL, lymphoedema or elephantiasis. At the community level, there was a strong positive correlation between the prevalence of antigenaemia and the prevalence of prolonged nocturnal cough (R2=0.35) in the 12 DS areas, supporting the likelihood of a filarial aetiology to this symptom. Although the prevalence of hydrocoele was low, there was also a strong positive correlation between this rate and antigenaemia rates in the communit (R2=0.56). Correlation between infection fates in C. quinquefasciatus and theprevalence of nocturnal cough and hydrocoele at DS area level was 0.04 and 0.40 respectively. Aggregation of CF A positive individuals within households was noted |
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