Graves, Patricia; Sheridan, Sarah; Fuimaono, Saipale D; Lau, Colleen
Background: Prevalence of lymphatic flariasis (LF) antigen in American Samoa was 16.5% in 1999. Seven rounds
of mass drug administration (MDA) programmes between 2000 and 2006 reduced antigen prevalence to 2.3%. The
most efcient methods of surveillance after MDA are not clear, but testing specifc at-risk groups such as adults may
provide earlier warning of resurgence. The role of migration from LF endemic countries in maintaining transmission
also needs investigation. Few studies have...[Show more] investigated knowledge about LF and how that relates to infection risk.
This study aims to investigate associations between socio-demographics, population mobility, disease knowledge
and LF infection risk.
Methods: In 2014, we surveyed 670 adults aged 16–68 years (62% female) at two worksites in American Samoa. Sera
were tested for LF antigen and antibodies (Bm14 and Wb123) by rapid test and/or ELISA. Multivariate logistic regression was used to assess association between seromarkers and demographic factors, household socioeconomic status
(SES), residence, travel history, and knowledge of LF.
Results: Overall, 1.8% of participants were positive for antigen, 11.8% for Bm14, 11.3% for Wb123 and 17.3% for at
least one antibody. Recent travel outside American Samoa was not associated with positivity for any seromarker. Men
had higher seroprevalence than women for all outcomes (any antibody: adjusted odds ratio (aOR)=3.49 (95% CI:
2.21–5.49). Those aged over 35 years (compared to 15–24 years) had higher prevalence of Bm14 antibody (aOR=3.75,
3.76 and 4.17 for ages 35–44, 45–54 and ≥55 years, respectively, P<0.05). Lower SES was associated with seropositivity (antigen: aOR=2.89, 95% CI: 1.09–7.69; either antibody: aOR=1.51, 95% CI: 1.12–2.05). Those who knew that
mosquitoes transmitted LF had lower Wb123 antibody prevalence (aOR=0.55, 95% CI: 0.32–0.95).
Conclusions: Opportunistic sampling of adults at worksites provided an efcient and representative way to assess
prevalence and risk factors for LF in American Samoa and in hindsight, foreshadowed the resurgence of transmission. Risk of LF infection, detected by one or more serological markers, was not related to recent travel history, but
was strongly associated with male gender, older age, lower SES, and lack of knowledge about mosquito transmission.
These results could guide future eforts to increase MDA participation.
Keywords: Lymphatic flariasis, American Samoa, Population mobility, Socioeconomic status, Disease knowledge,
Sero-epidemiology, Surveillance, Mosquito
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