Sustained mumps transmission in a highly vaccinated population
Abstract number: O255
Wohoush M., Obeidi M., Hindiyeh M., Riccardo F., Sabatinelli G.
Objectives: To describe a parotitis outbreak in a highly vaccinated population of Palestine refugees in West Bank (WB).
Methods: The United Nations Relief and Works Agency (UNRWA) surveillance system targets various diseases including mumps. In December 2003, following an increase in the reported incidence of mumps among WB Palestinian refugees, an outbreak line listing was established, serum IgM and IgG test was adopted for confirmation and RT-PCR for differential diagnosis and parotitis virus isolation. The immunisation status of patients was assessed from immunisation cards. Univariate analysis was performed and attack rates calculated.
Results: On average 3 cases meeting the WHO clinical case definition for mumps are reported each month from WB (670,613 refugees of whom 176,726 living in 19 refugee camps). When 5 mumps cases were reported from a single camp in northern WB in December 2003 the system was alerted. In 2004 and 2005, mumps cases increased by more than 4 folds the baseline. The epidemic started in north-eastern WB (Nablus) spread westwards and extended to central WB (Jerusalem). Only one case was reported in 2005 in southern WB (Hebron). A total of 3928 cases were detected (males 56%, mean age 11.7±7 years, 70.8% in the 615 years age group). Attack rates in the camps varied between 0.03% and 4.3% (overall 1.2%). Complications were reported in 1% of cases and all outcomes were favourable. UNRWA introduced MMR vaccination (single dose) in 1988. 67.5% of all patients and 80% of those born after 1988 had been immunised at least one month before the onset of symptoms. 6 year-olds in 2004 and 7 year-olds in 2005 were the mostly affected age groups suggesting a cohort effect for vaccinated in 1999 (Fig.) moreover almost 30% of all vaccinated patients had been immunised between 1999 and 2000. In order to control the outbreak an MMR vaccination campaign was conducted in May 2005 targeting 58,561 students from UNRWA schools and vocational training centres (coverage 96%). In 2006 and 2007 cases dropped below the outbreak threshold line but settled at higher than pre-outbreak levels.
Conclusions: High immunisation coverage did not prevent the parotitis outbreak although complications seemed to occur more rarely than expected. Although preliminary data suggests a cohort effect pointing to a problem occurred during a specific vaccination year, further investigations are planned to explain this event and avoid future epidemics.
|Session name:||18th European Congress of Clinical Microbiology and Infectious Diseases|
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