Slapped cheek disease is caused by a human virus called parvovirus B19. The virus is passed on by an infected person, mainly through coughing or sneezing. Symptoms start from 4–20 days after you are infected with the virus.
You can pass the virus on to others from 5–6 days before symptoms start. Once the rash appears, you are no longer infectious.
Slapped cheek disease is most common during winter and spring. It spreads rapidly through schools because it is infectious before you have any symptoms.
Only a small number of adults get slapped cheek disease. Many adults are already immune because they had the virus in the past, maybe without realising. Your body produces antibodies to the virus which protects you from getting it more than once.
Very rarely, unborn babies can be infected through their mother’s blood during the first 20 weeks of pregnancy. This creates a small risk of miscarriage or your baby getting a type of anaemia (low iron levels in the blood).