Measles laboratory-based surveillance in Zimbabwe during 2004-2009

Zimbabwe has for a long time satisfied measles elimination criteria according to the World Health Organization Regional Office for Africa (WHO/AFRO) measles surveillance standards. In this elimination phase laboratory based surveillance becomes critical as it gives evidence on the interruption of transmission of measles virus in the country hence the performance of the laboratory has to be monitored.

This retrospective study assesses measles laboratory performance in Zimbabwe from 2004 to 2009 by monitoring laboratory surveillance quality indicators against predefined WHO indicators.

Overall, 92.20% of serum specimens arrived in the laboratory in good condition, 66.8% were received in the lab within the stipulated three days and 77% of the results were sent back to the national centers within 7 days. The laboratory passed all external proficiency tests from 2005 to 2009 with 100%. The laboratory sent 13.42% of representative sera for regional reference laboratory co-testing and the concordance of results was 98.33%. An average of 27.33% of patients with positive measles IgM had vaccination history.

Available data shows that four out of the six WHO surveillance indicators were met by the national laboratory. The timeliness of specimen shipment to the lab needs to be improved and results should be communicated to the national centers in a timely manner. Cases with no vaccination history may be due to incompletely filled out forms or inadequate case investigation. Unvaccinated cases can accumulate over time and cause outbreaks.

The results of the external proficiency tests show that the laboratory is performing well, with adherence to quality requirements, as indicated by proficiency tests with the regional reference laboratory. Hence the results generated by the laboratory may be reliable for surveillance.