Human parvovirus B19 is a seasonal virus spread mainly through the air. Most people catch it in their school years and are then immune for life; the share of people with protective antibodies rises from about 50% at age 20 to about 70% by 40. It can also pass from mother to fetus, and rarely through blood transfusions or some plasma products. There is no vaccine and no antiviral.
For most people it's a mild respiratory illness. But it can be serious for three groups:
| Group | Risk |
|---|---|
| Pregnant people | infection of the fetus, which can cause fetal anemia, hydrops fetalis, and pregnancy loss in 5%–10% of cases |
| People with chronic hemolytic blood disorders — sickle cell disease, thalassemia, hereditary spherocytosis | transient aplastic anemia: low hemoglobin with too few new red cells |
| People with certain immune-weakening conditions, such as blood cancers | persistent aplastic anemia |
In early 2024, several European countries reported a sharp rise in B19. The United States has no routine surveillance, so CDC and Labcorp checked two independent data streams from January 2018 to August 2024.
What the lab data showed
Patients tested by their doctors
Labcorp tested 399,098 specimens from 359,445 people for B19 IgM antibodies, a sign of recent infection. Most came from adults (92.6%), and most adult specimens from women (87.7%) — many adults tested were aged 30–39.
B19 normally peaks in the second quarter (April–June). It nearly vanished during the pandemic, began climbing in the second half of 2023, and by Q2 2024 was well above earlier peaks:
| IgM-positive, second quarter | 2018 | 2019 | 2024 |
|---|---|---|---|
| All specimens | 3.8% | 5.1% | 9.9% |
| Children and teens | 10.7% | 15.6% | 24.9% |
| Adults | 2.9% | 4.0% | 5.1% |
The overall figure had stayed below 1.5% during 2020–2023.
- Highest among children aged 6–8 (39.9%) and 9–11 (34.3%) in Q2 2024.
- Among adults, highest at 40–49 (12.9%); adults 40–59 had more positive tests than in earlier years, while most other adult age groups returned to pre-pandemic levels.
- Every HHS region saw an increase, with the highest Q2 2024 positivity in Region 5 (Illinois, Indiana, Michigan, Minnesota, Ohio, Wisconsin; 11.2%), Region 10 (Alaska, Idaho, Oregon, Washington; 10.4%), Region 6 (Arkansas, Louisiana, New Mexico, Oklahoma, Texas; 10.0%) and Region 8 (Colorado, Montana, North Dakota, South Dakota, Utah, Wyoming; 9.1%).
- By the end of August 2024 the peak was declining, as in earlier seasons.
Children and adolescents: specimens tested for B19 IgM and share positive, by quarter (A) and age group (B), 2018–2024. CDC
Adults: specimens tested for B19 IgM and share positive, by quarter (A) and age group (B), 2018–2024. CDC
Healthy plasma donors
Labcorp also screens pooled source plasma — 512 donations per pool, about 1,059 pools a month — for B19 DNA. The share of pools above 1,000 IU/mL:
| Peak | Positive pools |
|---|---|
| 2018 | 6.7% |
| 2019 | 7.3% |
| 2020–2023 | under 2% |
| June 2024 | 20% |
Donor source plasma pools tested for B19 and share positive by nucleic acid testing, 2018–2024. CDC
Why 2024?
The rise showed up in two unrelated populations — sick patients tested by their doctors, and healthy plasma donors — which points to more community spread. The likely reason: pandemic precautions suppressed B19 for several years, leaving more people susceptible. Otherwise the pattern was familiar: a Q2 peak, with children aged 6–11 hit hardest.
What clinicians and the public should do
CDC issued a Health Advisory on August 13, 2024.
- Suspect B19 in people with fever, rash, joint pain, or unexplained anemia with a low reticulocyte count.
- Consider testing people at high risk of complications, including pregnant people who may have been exposed.
- Watch pregnancies closely: some European countries saw a significant rise in fetal illness and death several months after B19 spread widely. Look for reduced fetal movement or signs of hydrops.
- Groups at higher risk include people with leukemia or other cancers, organ transplants, HIV or current chemotherapy, and people with chronic hemolytic disorders.
- Everyone can cut spread with ordinary respiratory-virus measures: cleaner air (fresh outdoor air, air purification, gathering outside), good hygiene, masking, and school guidance. High-risk people who work or study where B19 exposure is likely might consider extra steps such as masking.
CDC is watching syndromic surveillance and health care databases for any rise in B19 complications.
Limits
One laboratory network, not deduplicated by patient, and changes in market share or ordering may affect volumes (though less so positivity). Little demographic data; testing depends on access to care and on doctors thinking of B19, so it may capture the more severe cases; plasma donors aren't representative of the population; and results couldn't be linked to outcomes.
Sources
Based on Alfego D, Hernandez-Romieu AC, Briggs-Hagen M, et al., "Detection of Increased Activity of Human Parvovirus B19 Using Commercial Laboratory Testing of Clinical Samples and Source Plasma Donor Pools — United States, 2024," MMWR volume 73, number 47, Centers for Disease Control and Prevention, with authors from Labcorp and CDC; a work of the United States government in the public domain. The report's text gives the 2018 and 2019 donor-pool peaks as 6.7% and 7.3% in one place and as 7% and 8% in another; the first pair is used here.
Licence: CC0 1.0 (public domain) · Adapted from www.cdc.gov
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