Erythema infectiosum, often referred to as fifth disease, is caused by human parvovirus B19 and occurs most often during the spring months, often in geographically limited outbreaks among children, particularly school age children. Infection is spread mainly by breathing in small droplets that have been breathed out by an infected person, so infection tends to spread within a household. The infection can also be transmitted from mother to fetus during pregnancy, rarely resulting in stillbirth or severe anemia and excess fluid and swelling (edema) in the fetus (hydrops fetalis).
Erythema infectiosum symptoms begin about 4 to 14 days after infection. Many children have no symptoms. However, some children have a low fever and feel mildly ill with a headache and a runny nose for a few days. Several days later, children develop red cheeks that often look like they have been slapped as well as a rash, especially on the arms, legs, and trunk but not usually on the palms or soles. The rash can be itchy and consists of raised, blotchy red areas and lacy patterns, particularly on areas of the arms not covered by clothing, because the rash may be worsened by exposure to sunlight.
The rash and the entire illness usually last 5 to 10 days. Over the next several weeks, the rash may temporarily reappear in response to sunlight, exercise, heat, fever, or emotional stress. In adolescents, mild joint pain and swelling may remain or come and go for weeks to months.
Erythema infectiosum can also manifest in a different way, particularly in children with sickle cell disease or other disorders of the red blood cells or in children with diseases that impair the immune system's ability to fight infection (such as acquired immunodeficiency syndrome [AIDS]—see Human Immunodeficiency Virus (HIV) Infection in Children). In these children, parvovirus B19 can affect the bone marrow and cause severe anemia.