Erythema infectiosum, commonly called fifth disease, is a viral infection caused by parvovirus B19 that produces a distinctive bright red rash on the cheeks, often described as a “slapped cheek” appearance. It primarily affects school-aged children and is usually mild, but it can cause serious complications during pregnancy or in people with certain blood disorders. The infection spreads through respiratory droplets, and most people are no longer contagious by the time the rash appears.
Why It’s Called Fifth Disease
Erythema infectiosum earned the nickname “fifth disease” because it was the fifth illness classified in a historic list of common childhood rash diseases. Unlike measles, rubella, and roseola, it rarely affects infants and instead shows up most often in school-aged children. Many adults have already been infected at some point in childhood without realizing it, since the illness can be so mild it goes unnoticed.
How It Spreads and When You’re Contagious
Parvovirus B19 spreads through respiratory droplets, much like a cold. The incubation period ranges from 4 to 21 days, and the most contagious window is the week before any symptoms appear. By the time the telltale rash shows up on the cheeks, the person is typically no longer infectious. This is why outbreaks move quickly through classrooms before anyone realizes what’s happening.
Because children are no longer spreading the virus once the rash is visible, there’s generally no need to keep them home from school after diagnosis. The illness is mild and self-limiting in most otherwise healthy people.
The Three Stages of the Rash
The infection progresses through three distinct skin phases, which is one of the features that makes it recognizable.
The first stage is the hallmark “slapped cheek” rash: bright red patches on both cheeks with notable paleness around the mouth. This facial rash doesn’t appear early in the illness. It shows up after the initial period of viral replication in the body, so by the time you see it, the worst of the infection has already passed. The facial rash typically lasts 4 to 5 days.
In the second stage, a bumpy, spotted rash spreads to the trunk and limbs, usually appearing a few days after the facial rash. This rash generally isn’t itchy and lasts about a week.
As the rash resolves in the third stage, it takes on a lacy, net-like pattern that’s most visible on the outer surfaces of the arms and legs. This lacy appearance can come and go for weeks, sometimes flaring up with sun exposure, warm baths, or physical activity, even after the infection itself has cleared.
How Parvovirus B19 Affects the Body
Before the rash appears, many people experience a mild flu-like phase with low-grade fever, headache, and body aches. This is the stage when the virus is actively multiplying in the bloodstream.
Parvovirus B19 has a specific target: it latches onto a receptor found on cells that are developing into red blood cells in the bone marrow. The virus temporarily disrupts red blood cell production. In healthy people, this pause is brief and harmless because existing red blood cells live long enough to carry the body through the interruption. But in people whose red blood cells are already short-lived or in short supply, the consequences can be severe.
Joint pain and swelling are common in adults, particularly women, and can linger for weeks or even months after the initial infection. Children, by contrast, tend to sail through with just the rash and perhaps a few days of feeling unwell.
Risks for People With Blood Disorders
For people with chronic anemias like sickle cell disease, parvovirus B19 can trigger what’s called a transient aplastic crisis. Because their red blood cells already break down faster than normal, even a brief halt in new red blood cell production leads to a dangerous drop in blood counts. The CDC has flagged this as a particular concern for children and adolescents with sickle cell disease.
A clinic-based report from Atlanta documented an increase in aplastic crises among young sickle cell patients tied to a surge in parvovirus B19 activity in 2024. The hallmarks of this complication are a noticeable drop in hemoglobin from baseline and a sharp decline in the immature red blood cells (reticulocytes) that the bone marrow normally pumps out. Early blood transfusions can prevent the most serious outcomes.
Risks During Pregnancy
Parvovirus B19 during pregnancy deserves special attention. When a pregnant person catches the virus for the first time, it crosses the placenta and reaches the fetus in roughly 30 to 50 percent of cases. The virus targets the same developing red blood cells in the fetus, which can lead to severe fetal anemia and a condition called hydrops fetalis, where fluid accumulates in the baby’s tissues and body cavities.
The risk is highest during the first and second trimesters. Ultrasound monitoring can detect early warning signs: fluid buildup in the abdomen is usually the first visible change, followed by fluid around the heart and later around the lungs. Bright-appearing bowel and an enlarged liver may appear even before fluid accumulation becomes obvious. In severe cases, intrauterine blood transfusion can be lifesaving for the fetus.
The CDC’s ongoing health advisory, first issued in August 2024, urges healthcare providers to maintain heightened awareness of parvovirus B19 in pregnant patients, especially given that transmission rates in 2025 have continued to outpace 2024 levels. Pregnant people who know they’ve been exposed or who develop symptoms consistent with fifth disease should be tested promptly.
Recent Surge in Cases
Parvovirus B19 activity dropped to low levels during the COVID-19 pandemic years of 2021 through 2023, likely because the same public health measures that slowed COVID also suppressed other respiratory viruses. In 2024, cases surged past prepandemic levels. The proportion of blood samples testing positive for recent infection peaked at 9.6 percent in late June 2024, up from a baseline of around 3 percent earlier that year.
Rather than settling back down, transmission has continued climbing. During the first five months of 2025, positive test rates were significantly higher than the same period in 2024, nearly double in the first quarter. This pattern of post-pandemic rebound is consistent with a larger pool of susceptible children who weren’t exposed during the years of reduced circulation.
How It’s Diagnosed
In a healthy child with the classic slapped-cheek rash, a doctor can often diagnose fifth disease on appearance alone. No blood test is needed.
When confirmation matters, particularly in pregnancy, in immunocompromised patients, or during an aplastic crisis, a blood test checks for specific antibodies. The presence of IgM antibodies is the most reliable marker of a recent or active infection, detected in about 97 percent of confirmed cases. These antibodies can persist for up to six months, so a positive IgM result indicates infection within the past several months rather than pinpointing the exact timing. IgG antibodies, by contrast, indicate past infection and lifelong immunity. Someone with IgG but no IgM was infected at some point in the past and is now protected.
Treatment and Recovery
For the vast majority of people, fifth disease needs no treatment beyond basic comfort measures. Rest, fluids, and over-the-counter pain relief for fever or joint discomfort are sufficient. The rash resolves on its own, and the lacy pattern that lingers on the arms and legs is cosmetic, not a sign of ongoing illness.
The picture changes for high-risk groups. People with sickle cell disease or other chronic anemias who develop an aplastic crisis may need blood transfusions to bridge the gap until the bone marrow recovers. Immunocompromised individuals who can’t clear the virus on their own sometimes develop chronic infection with persistent anemia. In these cases, immunoglobulin therapy can provide the antibodies their immune system isn’t producing, helping the body control the virus and allowing red blood cell production to resume.
There is currently no vaccine against parvovirus B19. Prevention relies on standard respiratory hygiene: frequent handwashing, avoiding shared utensils, and staying away from known cases if you’re pregnant or immunocompromised. The CDC has noted that wearing a mask around others is a reasonable extra precaution for those at elevated risk during periods of high community transmission.