Oral Fluid as Alternative Specimen to Serum in the Detection of Measles and Rubella Virus-Specific IGM Antibody by Enzyme Immunoassay in Kenya

Abstract

Measles is a severe, vaccine-preventable disease that causes extensive morbidity and mortality in large parts of the world. Despite the widespread use of measles vaccine, either as a single antigen vaccine or as a component of the triple vaccine against measles, mumps and rubella, 278 358 reported cases of measles and an estimated 164 000 deaths from measles occurred worldwide in 2008. Vaccine coverage is highly variable between World Health Organization global regions. Measles has been eliminated in the Americas but continues to be endemic in the African and South-East Asia regions, where vaccine coverage is less than 80%. These regions account for approximately 94% of all global measles deaths. In Kenya measles and rubella are still prevalent due to poor vaccination coverage in the neighboring war tone countries such as Somalia and Southern Sudan. Diagnosis of measles/rubella in a laboratory set up is usually done by serological examination of particular IgM from blood sample removed from the veins through puncture. The usual sample collection method is invasive hence not acceptable. There is need to develop and utilize a non-invasive sample collection technique such as saliva or oral fluid for diagnosis. This study was aimed at assessing the feasibility of oral fluid as an alternative method for the detection of measles/rubella-virus specific IgM in routine surveillance of measles and rubella. The study utilized a prospective laboratory based cross sectional design using matched serum/oral fluids which were collected during an emerging outbreak across Kenya of illness characterized by rashes. With a calculated sample size of 180 participants, only 176 participants enrolled and completed the study. Pairs of 176 samples were investigated by enzyme immunosorbent assay for IgM precise antibodies. The statistical analysis used was kappa (k) statistics to measure inter-observer variations. The occurrence of rubella was 26.7% and 23.3% when detected using serum and oral fluid methods, respectively. When tested against the gold standard (serum), specificity and sensitivity of rubella IgM in oral fluid was 93% and 86%, respectively. The prevalence of measles among the vaccinated participants was between 4.2% in Nairobi west, Nakuru North and Wajir East being the least and Nairobi North 45.8% being the highest. Nairobi north district recorded the highest percentage (male 33.3% and 66.7% female) because the region is occupied by refugees from Somalia and Southern Sudan. Rubella virus prevalence among the vaccinated participants was high compared to negative and indeterminate results combined. Nairobi North recorded the highest prevalence (64.3%) of rubella for the two genders while Wajir had the lowest prevalence (3.6%) among the vaccinated participants in all the Sub-Counties in this study. There was some degree of agreement between the two methods since the Kappa value was 0.80. On the other hand, prevalence of measles from oral fluid and serum was 39.8% and 31.8%, respectively. When tested against the gold standard, specificity and sensitivity of measles IgM in oral fluid was 97% and 96%, respectively. Kappa statistic value was 0.26 suggesting fair agreement between the two methods. The study concludes that the use of oral fluid specimen is the best alternative for measles/rubella diagnosis since it is simple to collect, non-invasive and more acceptable than serum. This alternative method can be applied in varied clinical set up and is more applicable to disease surveillance programs. The merit of oral fluids as a specimen for diagnosis is easy and safe to collect. It is also easily shipped to the laboratory. The results and findings of this study strongly suggest the use of saliva in conducting disease surveillance and epidemiological surveys and studies in Kenya.