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As the holiday season arrives, many are gathering with family and friends to celebrate. But, amid the cheer, there are a few unwanted guests making the rounds—infectious diseases.
According to Peter Chin-Hong, an infectious disease specialist at UC San Francisco, people should keep an eye out for the “Big Four”: three respiratory viruses—influenza, COVID-19, and RSV—and one gastrointestinal virus, norovirus. These pathogens are circulating at high levels across the U.S., making this a season of concern for public health.
Surge in Respiratory Viruses
The U.S. is currently experiencing high activity of the flu, COVID-19, and RSV. Data from WastewaterScan, an infectious disease monitoring network led by Stanford and Emory universities, shows that these viruses are widespread. COVID-19, in particular, is showing a sharp increase in several Eastern states, while the West remains relatively unaffected, with pockets of high transmission in cities like San Francisco, Seattle, and Boise. Chin-Hong notes that this could change as holiday travel helps spread these viruses across the country, a phenomenon he calls “the Great Holiday Equalizer.”
Flu activity is particularly concerning, as the virus has already begun spiking in other countries. In early December, the U.K. reported nearly four times the flu cases compared to last year, and South American nations like Chile, Ecuador, and Uruguay are seeing higher hospitalization rates. Chin-Hong suggests that the U.S. may follow a similar trajectory, despite the Centers for Disease Control and Prevention (CDC) predicting a low-impact flu season.
He attributes this discrepancy to the potential “carryover immunity” from last year’s flu season and widespread vaccination, though he cautions that it’s still uncertain how the season will unfold. This year, two strains of the flu—H1N1 and H3N2—are in circulation, with H3N2 linked to more severe disease. The current vaccine is expected to cover these strains, and Chin-Hong stresses that it’s never too late to get vaccinated.
The Threat of Bird Flu
Though the flu remains a top concern, there’s also the looming threat of H5N1 bird flu. While there’s no evidence suggesting human-to-human transmission, Chin-Hong advises caution around raw milk, eggs, and undercooked poultry, particularly as the virus continues to affect commercial poultry operations in the U.S.
COVID-19 and RSV Updates
COVID-19 remains a concern, particularly as it begins to show up in municipal wastewater at high levels. While cases are on the rise, Chin-Hong doesn’t anticipate a large surge in hospitalizations this year. He attributes this to “carryover immunity” from previous waves and the possibility that COVID has reached a plateau in some areas. However, the virus remains unpredictable, constantly evolving through recombinant variants, and Chin-Hong cautions that low vaccination rates could lead to future spikes.
Respiratory syncytial virus (RSV), which affects infants and the elderly, continues to circulate as well, adding to the overall respiratory burden. For all three of these viruses, Chin-Hong recommends the “Three Vs”: Vaccinate, ventilate, and wash hands often. Masks remain an effective measure when indoors or in close contact, but outdoor or well-ventilated settings are preferable.
Norovirus and Gastrointestinal Illnesses
Norovirus, a stomach virus that causes gastrointestinal distress, is another concern this season. Spread through contaminated surfaces or food, norovirus is notorious for quickly affecting multiple people. Chin-Hong highlights the importance of hand hygiene, especially when handling common surfaces like airplane trays, buffet serving spoons, or handrails. Keeping hands away from the face is also crucial in preventing infection.
Anecdotal reports suggest that norovirus is circulating widely, with many healthcare workers experiencing illness. In addition, other illnesses such as rhinovirus (common cold), pertussis (whooping cough), and walking pneumonia are making their rounds.
Stay Home If You’re Sick
As always, the best defense against spreading any infectious disease is isolation. Chin-Hong strongly encourages individuals who are feeling unwell to stay home and avoid gatherings, even if it means missing out on holiday festivities. By doing so, you can help prevent the spread of illnesses to others, ensuring that the season remains joyful for all.
As we celebrate the holidays, keeping an eye on health trends and taking precautions will help protect both ourselves and our loved ones from the infectious threats that tend to increase this time of year.
