The laboratory investigation of a measles outbreak in the eve of its elimination in Sri Lanka

Background: Measles is highly contagious and cause significant morbidity and mortality. Sri-Lanka has the goal to eliminate endogenous measles by 2020 in par with WHO. Objective: To describe laboratory confirmation and genotype distribution of measles cases during the outbreak occurred from mid-March to May 2019, Sri-Lanka Study design: This retrospective study was conducted at National Measles Reference Laboratory (NMRL), Sri-Lanka. All samples received were tested according to the testing flow chart at NMRL with WHO recommended kits. Blood samples were tested for anti-measles IgM and IgG with IgG avidity for IgG positives. Samples within 5days post-onset rash were tested with measles real-time RT-PCR. Products of genotyping PCR were sent to Regional Reference Laboratory, Thailand for sequencing. Subsequent phylogenetic analysis was done at NMRL. Data were analyzed by descriptive statistics. Results: A total of 182 blood and 46 throat/nasopharyngeal swabs were received from 195 suspected cases and 37(19 %) were positive for measles by anti-measles IgM, rRT-PCR or both. Majority was females, with mean age of 20 years. Cases represented three main geographical areas; Western-35 %, Central-32 % and Southern-27 %. High avidity IgG was detected in 27/37(73 %). Sequencing data of six cases (4 from Western and 2 from Central province) revealed genotype D8. Conclusion: Nineteen percent of the suspected patients were measles positive with 73 % having re-infections. Majority were 22 years or over. Measles genotype was D8 in two provinces, suggesting the spread of virus within the country. Laboratory confirmation with measles PCR; IgG avidity and sequencing/genetic analysis is critical in the verge of measles elimination.