An evaluation of two indirect fluorescent antibody tests for the diagnosis of Legionnaire's disease in South Africa.
The specificity and sensitivity of the indirect fluorescent antibody test (IFA) for the diagnosis of Legionnaires' disease in South African patients is unknown. Heat-treated and formalin-treated antigen preparations from 456 normal blood transfusion donors and from 34 confirmed patients with the disease (3 culture-positive cases and 31 cases of seroconversion) were assessed. Tests using both antigens showed a relatively high degree of positivity at low titres in normal individuals with an age-related increasing frequency of positive tests. The best combinations of specificity and sensitivity of the heat-treated antigen determinations were at titres of 1/128 and for formalin-treated antigen at titres of 1/8 for both IgG and IgM. An IgM titre of 1/8 using the formalin-treated antigen appeared to be the best diagnostic criterion of the IFA but an antibody level of 1/8 using this antigen was attained in only 37.1% of cases on initial testing but 100% of cases on subsequent testing.
MRC Emergent Pathogen Research Unit, School of Pathology, University of the Witwatersrand, RSA.
M E
ME
Ratshikhopha
K P
KP
Klugman
H J
HJ
Koornhof
D000328:Adult; D000367:Age Factors; D000907:Antibodies, Bacterial / Q000032:analysis; D005069:Evaluation Studies as Topic; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D007875:Legionella / Q000276:immunology; D007877:Legionnaires' Disease / Q000175:diagnosis*; D008297:Male
D000907:Antibodies, Bacterial