Ireland's infectious disease watchdog has alerted doctors to a sharp increase in cases of human parvovirus B19, or 'slapped cheek' disease.

This viral infection usually causes a mild, short illness but can result in complications in pregnant women and in patients with weak immune systems.

The Health Protection and Surveillance Centre (HPSC) recently recorded the highest number of parvovirus B19 infections in over a decade, with more than 180 patients testing positive during the first seven months of the year, compared to about 30 cases in 2011. A similar increase has also been reported in the UK.

The HPSC urged doctors to be extra vigilant and aware of guidance on diagnosis and management of infection. In addition, patients at risk of complications from the virus, and who display symptoms, should be investigated for the disease with out delay.

'Slapped cheek' disease is characterised by a distinctive bright red rash on the cheeks, which is how the condition got its name. Although this rash may appear to be quite dramatic, slapped cheek disease is usually a very mild condition that passes in a few days. Other symptoms include a mild fever and other flu-like symptoms, such as a sore throat and aches and pains.

The disease is usually mild, but in high-risk groups, such as non-immune pregnant women and people with blood abnormalities or a weakened immune system, the parvovirus B19 can cause a much more serious infection and trigger a range of complications.

The HPSC confirmed that about 60% of adults in Ireland, who would have had this infection as children, have lifelong immunity.

In women who become infected for the first time during pregnancy there is a 30% chance that the infection will be transmitted to the baby, then there is a very small risk of a miscarriage. This risk is much greater during the first half of pregnancy (1 in 10).

Slapped cheek disease is an airborne virus and spreads the same way as the cold or flu viruses through sneezing, coughing, kissing or close contact. It can be infectious between four to 20 days before the rash appears, at which point the person is no longer infectious. One in five people infected will have no symptoms at all.

Slapped cheek disease is also known as fifth disease because it's the fifth rash in a group of five red rash diseases that also includes scarlet fever, measles, rubella and roseola. It is most common in children aged four to 12 years, although it can affect anyone of any age.

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