SALIVARY DIAGNOSIS OF RUBELLA - A STUDY OF NOTIFIED CASES IN THE UNITED-KINGDOM, 1991-4

Rubella infections, notified by general practitioners on the basis of a clinical diagnosis, were investigated by testing blood and saliva sa mples for specific IgM. Overall 52 (29 %) of 178 cases with appropriat ely timed blood specimens were confirmed as recent rubella by IgM sero logy. Only 2 (3 %) of 74 cases in children under 5 years were confirme d compared to 50 (48 %) of 104 cases in older children and adults. The confirmation rate was lower (6 %) in those with documented vaccinatio n history than in those without (42%). The specificity of saliva rubel la IgM testing compared to testing corresponding blood samples was 99 %. The overall sensitivity of saliva rubella IgM testing was 81 %. Thi s rose to 90% if results from inappropriately timed specimens and spec imens taking more than 1 week to reach the laboratory were excluded. A corresponding saliva rubella IgG test was 98 % sensitive and 100% spe cific. Of 126 rubella IgM negative cases, 25 (20 %) were positive for parvovirus B19 IgM. This study confirmed that rubella surveillance bas ed on clinical reports is not specific. It also demonstrated that sali va samples, if taken 7-42 days after onset of illness and transported rapidly to the laboratory, are a feasible alternative to blood samples for rubella surveillance.