Measurement of tetanus antitoxin in oral fluid: a tool to conduct serosurveys.

BACKGROUND Serosurveys that measure tetanus antitoxin can complement immunization coverage surveys to allow evaluation of immunization services in developing countries. Measurement of IgG tetanus antitoxin in oral fluid was investigated as a practical and noninvasive alternative to and correlate of serum antibodies. METHODS Serum and oral fluid were collected from Malian infants, toddlers and adults (males without a history of tetanus vaccination). Specific IgG tetanus antitoxin was measured by enzyme-linked immunosorbent assay in serum (S-ELISA) and oral fluid (OF-ELISA). RESULTS One hundred forty-two pairs of serum and oral fluid samples were collected from infants, 35 pairs from toddlers and 35 pairs from adults. IgG tetanus antitoxin titers measured by OF-ELISA were 100-fold lower than those measured by S-ELISA but they correlated strongly (r = 0.90, P < 0.001). All 35 toddlers who had received 2 or 3 doses of diphtheria-tetanus-pertussis (DTP) vaccine (100%) had serum tetanus antitoxin levels >or=0.15 IU/mL and 28 of 35 (80%) had oral fluid values >or=0.0015 IU/mL. Among adults lacking a history of tetanus immunization, only 6 of 35 (17.1%) had serum titers >or=0.15 IU/mL and 4 of 35 (11%) had oral fluid titers >or=0.0015 IU/mL in oral fluid. CONCLUSIONS IgG tetanus antitoxin in oral fluid correlates well with levels in serum. OF-ELISA values >or=0.0015 IU/mL constitute protection against tetanus and in subjects >12 months of age imply multiple prior contacts with immunization services. IgG tetanus antitoxin measured by OF-ELISA provides a logistically practical alternative for performing seroprevalence surveys.