FIELD-EVALUATION OF AN IMMUNOGLOBULIN-G ANTI-F1 ENZYME-LINKED-IMMUNOSORBENT-ASSAY FOR SERODIAGNOSIS OF HUMAN PLAGUE IN MADAGASCAR

Bacteriological isolation of Yersinia pestis is the reference test for confirming plague infection, but recovery of the pathogen from human samples is usually very poor, When the etiology of the disease cannot be bacteriologically confirmed, it may be useful to possess alternativ e tests such as detection of specific circulating antibodies to help g uide the diagnosis. In the present study, the immunoglobulin G (IgG) a nti-F1 enzyme-linked immunosorbent assay (ELISA) has been applied to v arious human sera to evaluate its large-scale applicability in the hig h-endemicity plague foci of Madagascar. The sensitivity of the test wa s found to be 91.4%, and its specificity was 98.5%. The positive and n egative predictive values were 96 and 96.6%, respectively, Seroconvers ion was observed on day 7 after onset of the disease. Patients with a positive ELISA result could be separated into high (82%) and law (18%) IgG anti-Fl responders, Cross-reactions with eight other infectious d iseases prevalent in Madagascar were scarce and were found in 1 of 27 Mycobacterium tuberculosis-, 3 of 34 Schistosoma haematobium-, and 1 o f 41 Salmonella-infected patients. Finally, the efficiency of the IgG anti-Fl ELISA was evaluated during the MahaJanga, Madagascar, plague o utbreak of 1995. When the number of ELISA-positive patients was added to the number of bacteriologically confirmed and probable cases, the n umber of positive patients was increased by 35%. In conclusion, althou gh it does not replace bacteriology, IgG anti-Fl ELISA is a useful and powerful tool for retrospective diagnosis and epidemiological surveil lance of plague outbreaks.