A new CDC scoping literature review has shown that avian influenza infections in humans can be asymptomatic and can be transmitted person to person. The team identified 10 cases of 18 asymptomatic human H5N1 infections in which one member of a household contracted the infection through exposure to infected poultry, then a second member of the household contracted the virus having had no contact with sick or dead poultry.
Another article in the same journal discusses that with spillover into, and transmission among, other mammals (e.g., cats, dogs, mice, wild carnivores, swine, etc.), along with about 70 officially reported cases in humans. The traditional perception that human H5N1 infections are almost always symptomatic, with no human-to-human H5N1 spread, is being challenged.
Given the ongoing H5N1 outbreaks in animals, further study of such findings is critical for informing the actual public health risk of the virus and infection prevention guidance. Currently, testing for H5N1 consists of the collection of a respiratory or eye swab which is sent to a public health laboratory for specialized testing. These days, testing in the US is rarely authorized unless a person has been exposed to an infected animal or human and has symptoms such as fever, cough, or conjunctivitis. However, with asymptomatic cases having been detected and person-to-person transmission possible, this limitation should likely be revisited, to help ensure against the further transmission of the virus by those who don’t even know they are infected.
Public Health News:
- Respiratory syncytial virus (RSV) infections are increasing across the United States, leading to more hospitalizations among infants and toddlers. In October 2025, rates of ED visits were up 3x the rate from September.
- Likewise, in the European Union, although the overall number of patients with reported respiratory illnesses remains low, most countries are reporting an increase in influenza and RSV cases.
- The US CDC has reviewed relevant research and case reports of asymptomatic H5N1 infections in humans to better understand their frequency. Although these cases are rare, they are reported and typically detected via surveillance of contacts of persons with known exposures to H5N1. This review suggests that more routine surveillance of such contacts can assist in assessing overall risk and determining what additional public health preventive measures might be suggested.
- Measles cases in the U.S. continue to rise, reaching 1,648 confirmed infections this year, of which 87% are linked to outbreaks. The largest growth is in Arizona and Utah, which now report 138 cases, and upstate South Carolina, with 33 cases. Most infections are in unvaccinated children and teens, and 12% of patients have been hospitalized, with three deaths reported. Health officials are deploying mobile vaccination units to affected areas to increase protection.
- Los Angeles County reported its first West Nile virus death of the year, a San Fernando Valley resident who died from severe neurologic illness. Officials urge residents to use repellent, remove standing water, and repair window screens to prevent mosquito bites. So far, 14 cases have been reported in the county, half in the Valley. Peak mosquito season runs from June through November.
