Serodiagnosis of melioidosis in Singapore by the indirect haemagglutination test.

Melioidosis is endemic in Singapore, with diagnosis dependent upon both bacteriological culture and serodiagnosis. Using the polysaccharide (melioidin)-sensitized turkey red cells in the indirect haemagglutination test (IHAT), 20 (100%) of the Pseudomonas pseudomallei culture-positive cases were detectable by the IHAT with titles ranging from 1:16 to 1:32, 768. Eight of these patients who died within a few days after the IHAT was performed had titres ranging from 1:16 to 1:1028. Five culture-negative patients, with clinical symptoms suggestive of melioidosis infection and who responded to treatment with ceftazidime, showed IHA titres between 1:64 and 1:8,192. One hundred and twenty one sera from patients with pneumonia, abscesses, or diabetes mellitus were IHAT negative. The IHAT showed good specificity since negative titres were seen in tests using sera from 2 patients with culture-positive Pseudomonas aeruginosa and 4 patients positive for Legionella. IHAT negative results were obtained from tests of 50 normal blood donors and 50 sewerage workers. Of 683 national servicemen tested, 5 (0.73%) had IHAT titres ranging from 1:16 to 1:128. Unlike hyperendemic areas such as Thailand where interpretation of IHAT is seriously hampered by IHA titres found in one-third to half of the population, serodiagnosis of melioidosis by the sensitive IHAT may be employed in Singapore as a routine procedure since background IHA titres are low.