Some of us still need to consider masks in crowded places as covid and flu virus continue to spread.

At this point, Americans have had four years of thinking through winter virus safety. I hadn't planned to write another piece on the topic this year, but several readers wrote in with interesting questions that I thought others might want to consider.

"Pretty much everyone I know is enjoying their holiday without worry," wrote Mary in Virginia. "I am not in that same boat. My husband is waiting for a heart transplant. I am being treated for a blood cancer. We are not going out to restaurants. If the weather is nice, we'll visit friends in their yards. Our adult children aren't staying with us out of fear of giving viruses (not only covid) to us. Please can you remind people about the precautions that some of us still have to take?"

Mary and her husband are in the category of people who must continue to put many aspects of their lives on hold. Because they have severe underlying medical conditions including immunocompromise, they are especially vulnerable to covid, flu and other viruses. They are prudent to continue taking precautions, recognizing that doing so requires a lot of sacrifice.

Ingrid from Alabama asked where she can find up-to-date information about virus activity. "My housemate just got diagnosed with covid again, and I have several friends whose kids are out sick," she wrote. "Is virus season here?"

Yes, respiratory virus activity is increasing nationally, as shown by this helpful dashboard maintained by the Centers for Disease Control and Prevention. The CDC reports that the spread of acute respiratory illnesses severe enough to lead people to seek health care is "moderate" nationally. Both covid and seasonal flu activity are increasing, as is infection from respiratory syncytial virus (RSV). I expect these numbers to trend upward over the next month, consistent with past years.

"One thing I haven't seen you write about lately is masks," Lucas from Oregon wrote. "I was just on a plane, and I saw maybe four people wearing masks. You used to write that people should mask before going to visit high-risk family members. Do you still believe that?"

During the height of covid, many people asked me how they could safely visit vulnerable family members (or receive visitors if they were high-risk). What I advised at the time -- and what I still advise -- is that everyone should assess how important it is to avoid contracting covid and other respiratory illnesses.

If it's extremely important that certain individuals avoid infection, their visitors should try to reduce their risks in the days before the gathering. That would include wearing a high-quality, well-fitting N95 mask or something equivalent when in crowded settings such as airports and train stations. It should also include forgoing other social gatherings, monitoring for symptoms and taking a rapid test just before seeing the vulnerable person. Consider taking the recently approved rapid test for both covid and flu.

Molly from New York wrote that she and her entire family became sick last Christmas from a gastrointestinal illness. "No one found the source, but we don't want it to happen again," she wrote. "What's your advice for preventing illnesses spread by food?"

The most common cause of gastrointestinal illness is norovirus, a highly contagious virus spread by direct contact with an infected person. Norovirus outbreaks can affect an entire family within a short period, and it's possible this is what you all had last year. Good hand-washing can help reduce the risk of norovirus, as can making sure no one who is preparing food is experiencing diarrhea or other gastrointestinal symptoms.

There are also a number of bacteria that can cause foodborne illness, including E. coli, campylobacter and salmonella. You can avoid these pathogens by keeping hot food hot and cold food cold. There is a "danger zone" between 40 and 140 degrees Fahrenheit in which bacteria multiply rapidly. Perishable and cooked food shouldn't be left at room temperature for more than two hours. Either the food should be kept in a slow cooker or another appliance that keeps it above 140 degrees, or it should be refrigerated.

Be especially careful when cooking meat and fish. Use separate plates and utensils with raw meat and fish to prevent cross-contamination and an internal thermometer to monitor cooking progress. Fish should be cooked to an internal temperature of 145 degrees; ground meat and sausage to 160 degrees; and poultry to 165 degrees.

Speaking of raw products, Leslie from Washington is miffed by the "negative press" around raw milk, which she calls "astounding." "Not one case of bird flu has been linked to raw milk, yet I see these dire warnings from [federal health officials]," she wrote. "What's next, telling us not to eat raw eggs in our eggnog?"

I think what Leslie is referring to is that no human case of H5N1 infection has yet been traced to raw milk. But drinking raw milk is suspected to be a major route of transmission among animals; from a mother cow to its calf, for example, or between species. (For instance, farm cats have become infected after drinking raw cow's milk).

A recent analysis by the Food and Drug Administration found that 14 percent of raw milk samples taken from states with dairy herd outbreaks contained infectious H5N1. Bird flu is not the only infection concern. Before pasteurization was widely adopted, about 1 in 4 foodborne illnesses in the United States were related to dairy consumption. These days, listeria, campylobacter and other bacterial pathogens continue to sicken those who consume raw milk.

Pasteurization kills these bacteria. It also kills bird flu. I recommend following health officials' advice and sticking with pasteurized milk.

Eating or drinking raw egg also is not advised, as there is a chance of salmonella infection. Thankfully, there are many delicious eggnog recipes that don't contain raw egg. I hope Leslie can try some of these alternatives.