It’s that time of year, when families and friends come together to share their holiday cheer and a few circulating pathogens.

Peter Chin-Hong, an infectious disease specialist at UC San Francisco, said people should be on the lookout for the “Big Four”: three respiratory viruses currently moving through the U.S. — influenza, COVID-19 and RSV — and one stomach virus — norovirus.

According to WastewaterScan — an infectious disease monitoring network led by researchers at Stanford and Emory universities, with lab-testing partner Verily, Alphabet Inc.’s life sciences organization — those four viruses are running hot around the nation.

In the case of COVID-19, the half of the U.S. east of Montana, Wyoming, Colorado and New Mexico — is trending “high,” while the Western states are still generally low, with some hot spots in major cities such as San Francisco, Seattle, Salt Lake and Boise, according to WastewaterScan.

But that’s likely to change as holiday travel moves those viruses around in what Chin-Hong referred to as “the Great Holiday Equalizer.”

It’s flu, though, that is grabbing most physicians’ and researchers’ attention right now, he said.

While the federal Centers for Disease Control and Prevention‘s outlook for the severity of the flu‘s impact this season was low, Chin-Hong said he saw ominous signs coming from the typical bellwethers for the U.S.: the United Kingdom and South America.

In the UK, there were nearly four times the number of flu cases in early December than they were the same time last year. A similar trend occurred during the winter season in the South American nations of Chile, Ecuador and Uruguay, where hospitalizations were higher than in the 2023 flu season. Elsewhere on the southern continent, seasonal flu rates were fairly typical.

Chin-Hong suspects the CDC’s outlook is based on the assumption that people have some “carryover immunity” from last year, and he said vaccinations help.

But until flu season gets into full swing, it’s difficult to know exactly what it’ll look like and whether the vaccines have the circulating strains fully covered.

Chin-Hong said there are two predominant strains of the virus circulating: H1N1 and H3N2, with the latter virus associated with more severe disease, which may be causing the surges of hospitalizations abroad. But he said this year’s vaccine should cover it.

“It’s never too late” to get vaccinated, he said, noting that flu season in the U.S. is just beginning.

In addition, with the ominous threat of H5N1 bird flu simmering in the background, there is concern that it could mix with a human seasonal flu. Getting vaccinated and keeping the seasonal flu at bay, he said, will decrease the chances for such an occurrence.

Researchers and health officials say there is no evidence that H5N1 can be transmitted between people. But to keep extra safe as the virus moves through the nation’s dairy herds and commercial poultry operations, people should avoid raw milk, raw eggs and undercooked meat. Pasteurization and proper cooking techniques inactivate the virus.

But it’s not only the flu that’s threatening to dampen the nation’s good tidings.

COVID-19, RSV and norovirus are also prevalent.

COVID-19 has recently begun to show up in high levels in municipal wastewater, but Chin-Hong said that doesn’t necessarily mean we’ll see a surge in hospitalizations. Indeed, while the number of COVID cases is ticking up, the CDC predicts there will be fewer cases in the U.S. this year than in 2023.

“Some people think the reason why people are not getting it as much this year is because we got it so recently, particularly in California, and so that carryover immunity is kind of protecting us, at least for the time being,” Chin-Hong said. “The other hypothesis is that we just had enough cycles of it in the population, so maybe it kind of is low this year.”

But, he said, COVID has proven itself a nimble and adaptable virus, continually spawning recombinant variants, so “coupled with low vaccination rates, that’s always the fear with COVID, that it’ll surge back.”

The best things one can do to avoid the three respiratory viruses — influenza, COVID and RSV — is to follow “The three V’s: Vaccinate, ventilate and wash your hands very often,” he said. If you must be indoors or in close proximity to others, masks do make a difference. But try to mingle and cavort outdoors or in well-ventilated areas.

As for norovirus, which causes gastrointestinal distress and typically spreads via items handled by multiple people — such as airplane trays, handrails and buffet serving spoons — washing your hands is key. In addition, keeping your hands away from your face is critical; that’s the primary route of infection.

Chin-Hong said norovirus is seemingly everywhere these days.

“Anecdotally, a lot of colleagues of mine have been out with it,” he said.

In addition, there is some rhinovirus (common cold), pertussis and walking pneumonia circulating, he said.

And of course, he said, if you’re not feeling well, stay home. Nothing stops a virus or contagious bacteria is its tracks like keeping isolated — even if it means missing out on holiday revelries.

Gov. Gavin Newsom declared a state of emergency Wednesday as the H5N1 bird flu virus moved from the Central Valley to Southern California dairy herds, while federal officials confirmed the first U.S. case of severe illness in a hospitalized Louisiana patient — a concerning development as the virus continues to spread throughout the nation via migrating birds.

The declaration by Newsom will allow for a more streamlined approach among state and local agencies to tackle the virus, providing “flexibility around staffing, contracting, and other rules to support California’s evolving response,” according to a statement.

“Building on California’s testing and monitoring system — the largest in the nation — we are committed to further protecting public health, supporting our agriculture industry, and ensuring that Californians have access to accurate, up-to-date information,” Newsom said in the statement. “While the risk to the public remains low, we will continue to take all necessary steps to prevent the spread of this virus.”

According to the U.S. Department of Agriculture, 645 dairy herds in California have reportedly been infected with the H5N1 virus since August. Nationwide, the number is 865 and stretches back to March, when the virus was first detected in Texas herds.

There have also been a number of infections identified in pet cats in California, including three announced on Wednesday.

According to the CDC, 61 people have acquired the virus since March — the vast majority at dairies or commercial poultry operations. Most suffered from mild illness, including conjunctivitis, or pink eye, and upper respiratory irritation.

In California, 34 people have become infected with H5N1, with all but one contracting the virus from infected dairy. The outlier was a child in Alameda County; the source of that infection has not been determined. There was also a suspected case in a child from Marin County who drank raw milk known to be infected with the virus. The CDC was unable to confirm illness in that child.

The case in Louisiana is concerning to public health officials because of its severity. Federal officials would not provide details about the patient’s symptoms, deferring all inquiries to Louisiana’s Department of Public Health.

Emails and calls to that agency went unanswered.

According to CDC officials, the patient was reportedly in close contact with sick and dead birds from a backyard flock on the patient’s property. The virus was a version of the H5N1 bird flu that researchers have labeled D1.1 and is circulating in wild birds.

The strain circulating in dairy cows is known as B3.13.

It was the D1.1 version that was detected in a Canadian teenager hospitalized with severe illness in November. The source for that patient’s infection remains unknown.

According to Demetre Daskalakis, director of the CDC’s National Center for Immunization and Respiratory Diseases, Louisiana health officials and the CDC are investigating the patient’s contacts and performing further genetic analysis of the patient’s virus to determine what, if any, changes may have have occurred.

“These additional laboratory investigations help us to identify concerning changes in the virus, including changes that would signal an increased ability to infect humans, increased ability to be transmitted from person to person, or changes that would indicate that currently available diagnostics, antiviral treatments or candidate vaccine viruses may be less effective,” said Daskalakis in a news conference Wednesday morning.

He said analyses so far have not indicated changes in the virus that would make it “better adapted to infect or spread among humans.”

Analyses of the Canadian teen’s virus showed mutational changes that would make it easier for that version of H5N1 to infect people. However, it is unclear if those changes came prior to the infection — in the wild — or during the course of the child’s infection.

None of the child’s family members or contacts were infected, suggesting the changes occurred in the teenager during the infection and therefore the virus reached a dead end when it was unable to spread beyond the child.

These cases are akin to those recorded historically in Asia and the Middle East, where the H5N1 virus had resulted in a mortality rate of roughly 50%. Since the virus was first identified in 1997, there have been 948 cases reported worldwide leading to 464 deaths.

The cases associated with the B3.13 strain circulating in the nation’s dairy herds have so far resulted in only mild symptoms.

Still, research indicates that changes in at least one viral isolate taken from a dairy worker in Texas had acquired mutational changes that allowed for airborne transmission between mammals, and was 100% lethal in laboratory ferrets.

However, as in the case of the Canadian teen, it is believed that version was unique to the dairy worker and did not spread beyond.

Other research shows that only one mutational change is required for the B3.13 version to pass efficiently between people.

The D1.1 version of the virus “worries me a bit,” said Richard Webby, director of the World Health Organization’s Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds. “Not necessarily because I know it will evolve differently, but it does have a different combination of H5 and N1 which theoretically could help support a different set of mutations” than what researchers have seen in experiments with the B3.13 version.

Daskalakis said the CDC still considers the risk to the general population to be low, and the agency is working to expedite influenza and bird flu testing in clinical and public health laboratories “to help accelerate identification of such cases through its routine influenza surveillance.”

According to Newsom’s office, “California has already established the largest testing and monitoring system in the nation to respond to the outbreak.”

You might have heard of Lise Meitner. A native of Austria, she was the first woman to become a full professor of physics in Germany. She also helped discover nuclear fission. Yet the 1944 Nobel Prize for Chemistry for that accomplishment went solely to her longtime collaborator, Otto Hahn.

Meitner battled misogyny and sexism at every stage of her illustrious career. But growing antisemitism and the 1933 Nazi takeover of Germany were an even higher-order problem. Although she was a convert to Lutheranism, her Jewish heritage endangered her. With the help of friends, she was able to flee in 1938 to neutral Sweden, where she was safe but scientifically isolated. “I can never discuss my experiments with anyone who understands them,” she wrote to fellow physicist Hedwig Kohn.

In “Sisters in Science,” Olivia Campbell tells the intertwined stories of Meitner and three other notable, but lesser known, women physicists from Germany: Kohn, Hertha Sponer and Hildegard Stücklen. Only Kohn was Jewish, but the Third Reich’s hostility to women academics cost the other two jobs as well.

All three eventually made it to the United States, where they pursued their careers and continued to support one another (and Meitner too). Kohn, the last to escape, didn’t make it out of Europe until 1940. She endured two months of arduous travel through the Soviet Union and Japan and across the Pacific Ocean, barely surviving the ordeal.

Theirs is an inspiring tale, and well worth telling — all the more so because, as Campbell notes in her dedication, so many other women academics were murdered by the Nazis. “Their absence haunts this book; the rippling impact of their loss affects us all,” she writes.

But its intrinsic interest notwithstanding, “Sisters in Science” is a sometimes frustrating read. Part of the problem is its ambitious scope. Group biography is a tricky genre. Campbell has to meld four narrative arcs: parallel at times, overlapping at others, but also divergent. A more elegant stylist, or a true adept of narrative nonfiction, might have managed to integrate these stories more seamlessly. It doesn’t help that Campbell refers to her protagonists by their first names — and three of the four begin with the letter “H.”

Explaining the physics to a lay audience is another challenge, perhaps an insuperable one. Campbell attempts it only nominally. The idea of fission, the splitting of atomic nuclei and resulting production of vast amounts of energy, is more or less intelligible. But the accomplishments of the other three physicists, who worked in spectroscopy, optics and astrophysics, are harder to grasp.

The book also would have benefited from better copy editing and fact-checking. Whatever her bona fides as a science journalist, Campbell is not at home in Holocaust history. One example: Campbell locates Dachau, the Nazis’ first concentration camp, in Oranienburg, a suburb of Berlin. Dachau opened in 1933 in the town of Dachau, near Munich. Oranienburg was actually the site of another eponymous camp and then, in 1936, Sachsenhausen.

There are other errors and infelicities. Campbell continually refers to Kristallnacht, the November 1938 Nazi pogrom, as “the Kristallnacht.” A more serious lapse is her anachronistic suggestion that, in 1938, Meitner feared being deported to a “death camp.” Camps such as Dachau and Sachsenhausen were brutal, often murderous places, but in the 1930s, they mostly housed Nazi political opponents (some of them Jewish). Jews were not yet being deported from Germany, and the six death camps dedicated to their extermination — places such as Sobibor, Treblinka and Auschwitz-Birkenau, all in Poland — did not become operational until the early 1940s.

It is also somewhat crude, and arguably inaccurate, to say that Kristallnacht “exposed the Nazis’ true agenda for the Jewish people: they wanted them all dead.” Despite the growing virulence of anti-Jewish persecution, that goal was not yet clear, and not yet official policy. In fact, though some were killed, most of the 30,000 or so Jewish men rounded up and taken to concentration camps during Kristallnacht were released on the condition that they emigrate.

Presumably Campbell is on firmer ground elsewhere — in noting, for instance, the difficulties that women scientists faced in Germany, including fights for pay, lab space and recognition; and in emphasizing the ways that they, and a few sympathetic male colleagues, helped one another endure, flourish and eventually escape.

When she first became Hahn’s assistant in Berlin, for example, Meitner was exiled from the main lab and stuck in a basement workshop with no nearby restroom. She ultimately rose to head the physics department at Berlin’s Kaiser Wilhelm Institute for Chemistry, a post she retained even after her Nazi-era dismissal from the University of Berlin.

Some male scientists were dead set against women. Others, such as Max Planck, welcomed collaboration from only the most exceptional of their female peers. One heroic supporter of women in science was the Nobel laureate James Franck. A German Jew, he resigned his post at the University of Göttingen before he could be fired, immigrated to the United States via Denmark, and was later instrumental in aiding colleagues, including women, who remained behind.

Franck and Sponer, his onetime assistant, were especially close — both friends and scientific collaborators. After a stint at the University of Oslo, Sponer accepted a position at North Carolina’s Duke University in 1936, and began working with Edward Teller, the eventual creator of the hydrogen bomb, “on the vibrational excitation of polyatomic molecules by electron collisions.”

Only after Franck’s wife died in 1942 did his long-germinating romance with Sponer come to fruition. He remained at the University of Chicago, and she at Duke. But in 1946, they married, and in Campbell’s sympathetic telling, experienced true happiness amid the sorrows around them.

Julia M. Klein is a cultural reporter and critic in Philadelphia.