The stomach bug that causes people, especially children and older adults, to vomit and suffer from diarrhea is sweeping across Connecticut, say infectious disease doctors.

So wash your hands and keep things clean with bleach when possible, they advise.

Norovirus, which appears every winter, appears to be peaking now, according to Dr. Scott Roberts, associate medical director for infection prevention at Yale New Haven Hospital.

“Last year it looks like we peaked in March, so maybe that will happen again. Time will tell,” Roberts said. “But we are hearing anecdotal reports of patients with norovirus certainly in the pediatric setting, and our lab data is reflecting that.”

Roberts said that so far cases were worse last winter, though this past December saw a higher peak.

“It seems so far it’s not as bad as last year, although it seems like we’re still on the upward trend, so I don’t know where this is going to peak,” he said.

The virus is spreading throughout the Northeast and mid-Atlantic states, as well as in Michigan and in the West, according to Dr. Ulysses Wu, chief epidemiologist and system director for infectious diseases for Hartford HealthCare.

“The place where you may have heard about it the most was cruise ships,” Wu said. “We see this in closed settings, military settings, college campuses, nursing homes and schools and daycares.”

Norovirus is “the most common cause of epidemic gastrointestinal disease across the world,” he said.

“There’s about 900 deaths a year in the United States and the majority of them are over age 65,” Wu said. “There’s probably 450,000 (Emergency Department) visits due to norovirus every single year as well.”

Roberts said unlike other viruses, norovirus “takes very few viral particles to actually cause infection, even in the single digits. A single virus can cause infection.”

Also, Purell and other alcohol-based sanitizers won’t kill the virus, Roberts said.

“It really requires specialized cleaners, such as bleach, to kill it,” he said. “So it’s hard to find it once it sets up shop in a congregate setting.”

Unlike E. coli or salmonella, in which diarrhea is the primary symptom, vomiting is the key symptom for norovirus, although diarrhea can come with it too, Roberts said. It will start “within 12 to 48 hours after exposure, so usually it’s pretty quick after seeing somebody sick,” Roberts said.

“If somebody tells me, Hey, you know, I had some egg salad at a picnic, (and) one day later, everybody’s vomiting, you know for sure that’s norovirus,” he said.

To keep from getting sick, “the key is you want to avoid them when they’re sick,” Roberts said. “Wash your hands with soap and water and disinfect the surfaces after they use them. Try to use separate bathrooms if somebody’s infected in your house.”

The way the virus spreads is from fecal contact and unwashed food, so make sure door knobs and countertops are cleaned with bleach and that food is well cooked, Roberts said.

“I would just emphasize food safety so washing hands and then heating up the food in the microwave to the point of sizzling hot and making sure your food is cooked and and maintained in a safe way, and then avoiding others who are known to be sick with gastrointestinal diseases,” he said.

People are not contagious until they begin vomiting, Roberts said, but they can shed virus for a couple of days after symptoms end.

“You really need to be asymptomatic for 72 hours before you even think about going anywhere or sending your kids back to school,” Wu said.