Norovirus cases in the city exploded this winter, trouncing rates of the stomach flu in previous years, new data shows.
December saw 1,264 recorded cases of the virus in the five boroughs, a more than 250% increase over the same period in 2023 and 2022, when just 488 and 470 cases, respectively, were reported, according to the latest figures provided by the city Department of Health and Mental Hygiene. The numbers have been on the rise at least since October, when 446 cases were reported, more than double the levels of the last two years, the figures show.
While case numbers of the virus, which is spread through contact with infected people, contaminated surfaces and foods, typically rise as the weather gets colder, the leap this winter is “very impressive,” said Dr. Jessica Justman, an infectious disease specialist and professor of epidemiology at Columbia Mailman School of Public Health. The numbers could be a reflection of changing behavior in the post-pandemic city – where hand sanitizer has become so ubiquitous that some might be using it instead of the more effective soap and water – though comprehensive data is lacking, she said. People may also be less prone to isolation in the years since the first wave of Covid-19.
Several factors could contribute to higher infection rates and there is likely not just one smoking gun, Justman said. For one, norovirus is incredibly easy to transmit, requiring only a small number of viral particles to spread. At the same time, those particles are very durable, able to cling to a surface like a kitchen counter or bathroom doorknob for a long time. That’s because they lack an outer coating of fat, which is what gets broken down and neutralized by alcohol and other detergents, she explained.
“We often want to find one simple fact that explains this type of outbreak and often that doesn’t exist,” Justman said.
The total number of infections is likely much higher than reported because not everyone with the virus will see a doctor and providers are not required to report cases unless they are part of a suspected outbreak, said Health Department spokeswoman Chantal Gomez. Public health officials do not know what is driving the increase and there has been no change in the way cases are reported, she said.
The city receives grant funding for general gastrointestinal disease surveillance from the federal Centers for Disease Control and Prevention, though there is no specific earmark for norovirus and minimal federal money for norovirus lab testing, Gomez said.
The number of infections appears to be on the rise nationally, though case data is incomplete. Across the 14 states reporting to the CDC (which do not include New York), there were 91 cases the week of Dec. 5, more than double the highest case count for that week in the preceding four years.
The state Department of Health does not collect data on individual cases but does monitor outbreaks when they are voluntarily reported by counties, said spokeswoman Danielle DeSouza. The state is tracking multiple investigations into local outbreaks of gastrointestinal illness, some of which are confirmed to be caused by norovirus, she said.
Most infections do not result in hospitalization and the public health guidance follows tips for preventing other types of winter infections, like influenza: wash hands with soap and water, regularly disinfect surfaces and stay home if you are sick.
