Ireland experienced a four-fold increase in mumps cases during the outbreak that occurred in 2008–2009 compared with outbreaks in previous years, public health scientists have found. The virus struck men more than women and affected more people aged over 30 than usual.

 

“The 2008–2009 mumps outbreak in Ireland has been the largest since the introduction of the MMR [measles, mumps and rubella] childhood vaccination schedule in 1988,” write Michael Carr and colleagues in the August issue of the Journal of Clinical Microbiology. A “strong bias” for acute infection with the mumps virus was observed in men compared with women, independently of vaccination status.

 

Mumps symptoms are normally benign but complications can occur, with about 10% of cases requiring hospital treatment. Complications can include pancreatitis and meningoencephalitis, which can result in deafness and other severe neurological affects.

 

The authors analysed genetic, virological and epidemiological features of viruses isolated from people diagnosed with mumps in Ireland between January 2004 and June 2009. In that period 1602 oral fluid samples and 7805 serum samples were submitted to the National Virus Reference Library at University College Dublin to confirm the presence of mumps.

 

The results showed that the majority of cases of the disease confirmed during the most recent outbreak in 2008–2009 occurred in young adults between the ages of 18 and 24. Before the MMR vaccine was launched in Ireland, mumps occurred mainly in children aged between five and 15.

 

Figures from the UK Health Protection Agency show that the majority of mumps cases recorded in England and Wales during 2008 and 2009 were in the 15–24 age group. Other studies have also shown an upsurge in cases in young people at colleges and universities, according to the authors.

 

This contrasts with findings from the USA, where the peak in age-specific attack rates has shifted from 5–9 years to 18–24 years of age and back again, they say.

 

In 2007, the latest year for which data were available, children from five to 14 years were the most affected age group in the European Union, according to the European Centre for Disease Prevention and Control.

 

Yet Carr and his colleagues note a “dramatic” rise in the number of people aged 30 and older presenting with mumps infection.

 

“The reasons for this finding remain unclear and may include incomplete vaccination… increase in overseas travel and the attendance at mass gatherings similar to the crowded conditions existing at colleges,” write the authors.