Citing the H5N1 threat, the CDC is pushing for peak flu monitoring this summer

TThe Centers for Disease Control and Prevention asked local and state health officials Tuesday to maintain flu surveillance operations at peak season levels through the summer, in an effort to remain vigilant for signs of human-to-human spread of the H5N1 bird flu virus.

Flu surveillance activities are generally conducted at low levels during the late spring and summer months, taking into account that as temperatures rise, transmission of seasonal flu viruses in the Northern Hemisphere falls to minimal levels.

But in a call with state and local health authorities, Nirav Shah, the CDC’s principal deputy director, said flu surveillance efforts this summer should not take place out of season, given the need to track human infections with H5N1, if that’s the case. is the case. occurs.

“The bottom line is that in light of the ongoing outbreak of H5 among domestic dairy cattle, we want to maximize our chances of detecting a case of new influenza in the community and minimize the risk of a case of H5N1 going undetected would remain in the community. ,” Shah told STAT in an interview after his call with leaders of the Association of State and Territorial Health Officials, the Association of Public Health Laboratories, the Big Cities Health Coalition, the Council of State and Territorial Epidemiologists, and the National Association of County. and city health officials.

Shah asked jurisdictions to increase the number of positive influenza virus samples they submit to public health laboratories for subtyping, a form of testing that detects the precise type of influenza virus a positive sample contains.

“We are saying that we do not believe there are cases of new H5 flu circulating because we have not seen any evidence that would indicate that. But until and unless we improve our subtyping, we are basing that conclusion on negative implications rather than confirmatory data,” Shah said in the interview.

He estimated that approximately 600 to 700 positive samples per week will be collected nationally over the summer that can be subtyped. During the meeting with representatives from state and local health agencies and testing labs, no one expressed concern about having to do the extra work, Shah said.

The outbreak, the first time H5N1 has been observed in dairy cattle, has been detected in 51 herds in nine states over the past two months. Scientists studying the phenomenon believe the virus is much more widespread. But farmers’ reluctance to cooperate in surveys has hampered efforts to estimate how far the virus has spread and how many people may have been infected.

So far, only one human infection has been identified, in a man who worked on a dairy farm in Texas. The man developed conjunctivitis, the only observable sign that he was infected.

H5N1 is a virus that originated in wild ducks. But over the past 27 years, the disease has spread around the world, killing hundreds of millions of poultry and a variety of mammal species, including seals, bears, raccoons and cats, both large and domestic. So far it has not been seen in cows.

Although it does not kill livestock, the presence of the virus in a species with which humans have regular contact is concerning because it gives the virus more opportunities to evolve and become better at spreading from mammal to mammal, possibly even from human to human . scatter. If it gains that capacity, it could cause a pandemic.

In addition to maintaining flu surveillance systems throughout the summer, the CDC and others use the detection of influenza A viruses in wastewater to look for places where the H5N1 virus may be spreading. H5N1 is an influenza A virus; this also applies to the H3N2 and H1N1 viruses that circulate during the flu season. But because the latter two typically circulate at very low levels in the summer, it is thought that detecting influenza A in wastewater could signal the presence of H5N1 in a community – whether in wild birds, cows, milk from an affected farm or people. .