A wide array of pathogens can cause gastrointestinal illnesses, including bacteria, viruses, and parasites. Here are a few pathogens that demonstrate the variety of seasonality and transmission trends among these pathogens:
Norovirus is a very contagious virus that causes vomiting and diarrhea. Anyone can get infected and sick with norovirus. Some of the possible transmission methods for norovirus are direct contact with an infected person, consuming contaminated food or water, or touching contaminated surfaces and then putting your unwashed hands in your mouth. Norovirus can spread extremely easily; people with norovirus illness can shed billions of norovirus particles—and it only takes a few virus particles to make other people sick.1
According to the CDC, “Norovirus illnesses and outbreaks are usually more common in cooler winter months. The majority of all outbreaks occur from November to April in countries above the equator, and from May to September in countries below the equator.”2 Data from BIOFIRE Trend shows norovirus reaching a peak in March-April for the past two years.