Laboratory diagnosis, molecular characteristics, epidemiological and clinical features of an outbreak of measles in a low incidence population in Australia.

Background: Prompt and accurate laboratory diagnosis of measles is essential for case detection, outbreak management and ongoing surveillance in low incidence countries. Several disease markers are employed for diagnosis and are important to determine epidemiological and molecular characteristics for future control measures.

Objectives: To report different disease markers, genotypes and epidemiology of a measles outbreak in Australia, a low incidence country.

Study Design: A retrospective descriptive study of the clinical and epidemiological features and laboratory diagnosis in 16 confirmed measles cases using measles serum IgM/IgG, antigen detection (IFA), viral RNA detection by real-time PCR and genotyping results for respiratory and urine specimens processed in one reference laboratory.

Results: Of the 16 confirmed measles cases, 11 were young adults aged between 20-35 years and 15 were not age-appropriately vaccinated. The most common genotype detected was D9 (11/16), followed by D4 (1/16) and D8 (1/16). Two imported cases were from the Philippines (D4) and Italy (D9). Of six disease markers, respiratory swab PCR and serum IgM gave the highest percentage (100%) of positive samples for confirmed cases followed by urine PCR (90.9%), serum PCR (66.6%), urine IFA (54.5%) and respiratory IFA (46.2%).

Conclusions: Measles should be considered in the differential diagnosis of a presentation with fever and rash, even in countries in the elimination phase of measles control. Genotyping is a powerful molecular-epidemiological tool to assist low incidence countries towards eradication goals. Improving vaccination coverage remains essential, particularly in young adults and travellers.