Seroprevalence and spatial epidemiology of Lymphatic Filariasis in American Samoa after successful mass drug administration.
BACKGROUND
As part of the Global Programme to Eliminate Lymphatic Filariasis (LF), American Samoa conducted mass drug administration (MDA) from 2000-2006, and passed transmission assessment surveys in 2011-2012. We examined the seroprevalence and spatial epidemiology of LF post-MDA to inform strategies for ongoing surveillance and to reduce resurgence risk.


METHODS
ELISA for LF antigen (Og4C3) and antibodies (Wb123, Bm14) were performed on a geo-referenced serum bank of 807 adults collected in 2010. Risk factors assessed for association with sero-positivity included age, sex, years lived in American Samoa, and occupation. Geographic clustering of serological indicators was investigated to identify spatial dependence and household-level clustering.


RESULTS
Og4C3 antigen of >128 units (positive) were found in 0.75% (95% CI 0.3-1.6%) of participants, and >32 units (equivocal plus positive) in 3.2% (95% CI 0.6-4.7%). Seroprevalence of Wb123 and Bm14 antibodies were 8.1% (95% CI 6.3-10.2%) and 17.9% (95% CI 15.3-20.7%) respectively. Antigen-positive individuals were identified in all ages, and antibody prevalence higher in older ages. Prevalence was higher in males, and inversely associated with years lived in American Samoa. Spatial distribution of individuals varied significantly with positive and equivocal levels of Og4C3 antigen, but not with antibodies. Using Og4C3 cutoff points of >128 units and >32 units, average cluster sizes were 1,242 m and 1,498 m, and geographical proximity of households explained 85% and 62% of the spatial variation respectively.


CONCLUSIONS
High-risk populations for LF in American Samoa include adult males and recent migrants. We identified locations and estimated the size of possible residual foci of antigen-positive adults, demonstrating the value of spatial analysis in post-MDA surveillance. Strategies to monitor cluster residents and high-risk groups are needed to reduce resurgence risk. Further research is required to quantify factors contributing to LF transmission at the last stages of elimination to ensure that programme achievements are sustained.
WHO Collaborating Centre for Children's Health and Environment, Queensland Children's Medical Research Institute, The University of Queensland, Brisbane, Australia; Research School of Population Health, Australian National University, Canberra, Australia.
Colleen L
CL
Lau
Centers for Disease Control and Prevention, Division of Parasitic Diseases and Malaria, Atlanta, Georgia, United States of America.
Kimberly Y
KY
Won
WHO Collaborating Centre for Lymphatic Filariasis, Soil-Transmitted Helminths, and other Neglected Tropical Diseases, Division of Tropical Health and Medicine, James Cook University, Cairns, Australia.
Luke
L
Becker
WHO Collaborating Centre for Children's Health and Environment, Queensland Children's Medical Research Institute, The University of Queensland, Brisbane, Australia; School of Veterinary Science, The University of Queensland, Gatton, Australia.
Ricardo J
RJ
Soares Magalhaes
American Samoa Department of Health, Pago Pago, American Samoa.
Saipale
S
Fuimaono
WHO Collaborating Centre for Lymphatic Filariasis, Soil-Transmitted Helminths, and other Neglected Tropical Diseases, Division of Tropical Health and Medicine, James Cook University, Cairns, Australia.
Wayne
W
Melrose
Centers for Disease Control and Prevention, Division of Parasitic Diseases and Malaria, Atlanta, Georgia, United States of America.
Patrick J
PJ
Lammie
WHO Collaborating Centre for Lymphatic Filariasis, Soil-Transmitted Helminths, and other Neglected Tropical Diseases, Division of Tropical Health and Medicine, James Cook University, Cairns, Australia.
Patricia M
PM
Graves
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018948:American Samoa / Q000453:epidemiology; D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood; D000947:Antigens, Helminth / Q000097:blood; D016000:Cluster Analysis; D004605:Elephantiasis, Filarial / Q000188:drug therapy / Q000453:epidemiology* / Q000517:prevention & control; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012306:Risk; D016036:Seroepidemiologic Studies; D062206:Spatial Analysis; D011795:Surveys and Questionnaires; D014958:Wuchereria bancrofti / Q000276:immunology*; D055815:Young Adult
D000909:Antibodies, Helminth; D000947:Antigens, Helminth