Fifth disease may be the most common infectious disease that most people have never heard of.
Millions of children in school and day care get Fifth disease each year, with the high-risk season - winter through spring - still ahead. About 50 percent of adults have had it. School and day care outbreaks are common, and it can affect entire classrooms.
Doctors used to dismiss Fifth disease as just another of those viruses that are always “going around.” Now they know it can cause serious problems in some individuals, including pregnant women.
Fifth disease was the fifth infectious childhood disease involving a red rash to be described by physicians. The others are scarlet fever, measles, rubella (German measles), and roseola.
At first, doctors didn't know much about the disease, and thought the name would be temporary, like “Disease X.” The name, however, stuck.
Doctors now know that Fifth disease is caused by infection with human parvovirus B19. Don't confuse it with the virus that pet dogs and cats are immunized against. They are different viruses. A human can't “catch” parvovirus from a pet, and a pet can't catch parvovirus B19 from an ill person.
Fifth disease usually is a mild illness that occurs in children. The ill child often develops a pinkish-red rash on the face, trunk of the body, and limbs. The facial rash has a “slapped-cheek” pattern, and Fifth disease once was called “Slapped Cheek Disease.” Some kids, however, have no noticeable symptoms.
There's no special treatment for Fifth disease in children who are in otherwise good health, and the rash usually disappears within 7 to 10 days.
The infectious period for Fifth disease differs from measles and other rash illnesses. It often results in kids being excluded from school or day care unnecessarily.
Children with most other rash-type infections can transmit the disease to others while the rash is visible. A child with Fifth disease is infectious before the rash appears, and can safely return to child care or school with the rash.
Fifth disease is very contagious. In child care or school outbreaks, for instance, 50 to 60 percent of children may get it. The disease is spread by sneezes, coughs, shared drinking cups or containers, and other contact with nasal mucus and saliva from an infected person.
Children who get Fifth disease usually will be immune for life.
Adults who are not immune also can get Fifth disease. Some have no obvious symptoms. Others develop the typical rash, joint pain and swelling, or both. Pain and swelling usually disappear within two weeks, but may last months.
Some people should be more concerned about infection with parvovirus B19.
It may cause serious illness in people with sickle-cell disease and other types of chronic anemia; cancer; human immunodeficiency virus (HIV) infection, and recipients of organ transplants.
Parvovirus B19 infection also may be a concern for a small number of pregnant women. At least 50 percent of women already are immune. The virus won't be a threat to their unborn child, according to the U.S. Centers for Disease Control and Prevention (CDC). In less than 5 percent of pregnancies, however, infection causes severe anemia in the unborn infant, and may result in a miscarriage.
CDC does not recommend that pregnant women routinely stay away from workplaces where Fifth disease outbreaks are under way. Rather, it says pregnant women should make the decision themselves, after discussions with their doctor and employer.
Michael Woods is the Blade's science editor. His column on health and medical issues appears each Monday. Email him at email@example.com.