Slapped cheek syndrome: fact sheet.
Slapped cheek syndrome is caused by a virus called parvovirus B19. Also known as "erythema infectiosum" or "fifth disease", it is a common childhood disease, and has become more common recently. It is a mild disease in children, causing a slapped cheek appearance. Interestingly, the rash occurs after the child stops being contagious (unless they also have a rare complication): a child with a rash is not contagious, but they may have been incubating the condition for the previous 4 to 20 days. As the illness is usually only diagnosed after the rash has appeared, there is seldom any reason to exclude children with the condition from school.
About 60% of us contract the condition as children, and this gives us life-long immunity to future episodes. People with immunity cannot catch the virus again.
Rarely, if a woman catches the virus while pregnant, the baby may also catch the virus. If a woman becomes infected before the first 20 weeks of pregnancy there is an increased risk of miscarriage of about 10%. Nothing can be done to prevent miscarriages due to parvovirus B19 infection.
Rarely parvovirus B19 infection may make the baby anaemic, which can cause a condition known as hydrops fetalis. Women who become infected between 9 and 20 weeks of pregnancy have a 3% risk of hydrops fetalis. This can cause a stillbirth. It can, however, be diagnosed from ultrasound scans, and treatment may prevent a stillbirth.
As most adult women are already immune to parvovirus B19, fewer than 1% of women who are exposed to the virus between 9 and 20 weeks of pregnancy will develop hydrops fetalis. (See appendix for details of this calculation.)
We recommend that women in the following categories should go to their GP to discuss having blood tests to see if they are already immune to the virus.
Women who should consider having blood tests for parvovirus B19.
The following women who should consider having blood tests: those who, while in the first 20 weeks of pregnancy -
have been in close contact with a case (defined as living in a household setting with a case; sharing a meal with a case; or being in the same room as a case for over an hour) OR
work (in contact with children) in a school or nursery where there is an outbreak of slapped cheek syndrome (defined as two or more cases in the same class or year group, or three or more cases in the school or nursery, with onset separated by less than three weeks).
Assume that, in the first half of pregnancy: (i) 60% of pregnant women are already immune to the virus; (ii) there is a 50% chance of becoming infected if exposed and non-immune; (iii) foetal hydrops develops in 3% of those infected between 9 and 20 weeks of pregnancy; and (iv) the excess risk of miscarriage in those infected before 20 weeks of pregnancy is 10%.
The probability of hydrops developing when a woman who is of unknown parvovirus B19 immue status, and is exposed to the virus between 9 and 20 weeks of pregnancy, is therefore:
0.4 x 0.5 x 0.03 = 0.006 or 0.6%.
Similarly, the excess risk of miscarriage in such a woman (in the first 20 weeks of pregnancy) is:
0.4 x 0.1 = 0.04 or 4%.
This page was put together by Dr Peter M B English, CCDC, Surrey Communicable Disease Control Service, and is based on a letter written by himself and Dr Malcolm Perkin, Specialist Registrar, Communicable Disease Surveillance Centre.