The UK's Covid lockdown appears to have had a massive impact on stomach bugs, slashing outbreaks by more than half in England during the first six months of the pandemic.
Far fewer people suffered vomiting and diarrhoea than usual, data show.
People staying at home, mixing less and washing their hands will have had an impact, say public health experts in a new article published by BMJ Open.
This perk may continue if we all carry on being more germ-aware, they say.
Routine surveillance in England shows the number of outbreaks caused by the winter vomiting bug norovirus has increased in recent weeks, although they are still below the five-year-average or usual level for this time of year.
Projectile vomiting
Norovirus is easily transmitted through contact with people who have it, or contaminated surfaces.
Prof Saheer Gharbia, from the UK Health Security Agency and one of the authors of the BMJ study, said: "Norovirus, commonly known as the winter vomiting bug, has been at lower levels than normal throughout the pandemic but, as people have begun to mix more, the numbers of outbreaks have started to increase again."
Symptoms include sudden onset of nausea, projectile vomiting and diarrhoea. Although it can be very unpleasant, it usually goes away in a couple of days.
The advice is to stay at home if you are experiencing norovirus symptoms and do not return to work or send children to school or nursery until 48 hours after symptoms have cleared.
Prof Gharbia said: "Please avoid visiting elderly relatives if you are unwell - particularly if they are in a care home or hospital.
"As with Covid and other infectious illnesses, handwashing is really important to help stop the spread of this bug, but remember, unlike for Covid, alcohol gels do not kill off norovirus, so soap and water is best."
For their study, Prof Gharbia and colleagues looked at information on outbreaks, laboratory notifications, calls to the NHS 111 health advice service, GP appointments, and attendance at emergency care for gastrointestinal infections during the first half of 2020 in England.
That included illness from bacteria like salmonella and listeria, as well as the winter vomiting virus.
Just over 1,500 suspected and lab-confirmed gastrointestinal infection outbreaks were reported in England, representing a 52% fall on the five-year average for the period.
Google Trends data showed internet searches for key phrases, such as "food poisoning", "gastroenteritis" and "sickness bug" plunged, while ones for "handwashing" and "disinfection" rose substantially during the UK's first Covid wave.
Each year in England there are typically more than 17 million cases of gastrointestinal infections, resulting in more than one million calls or visits for medical advice or care.
To help reduce the spread:
- *Wash your hands frequently and thoroughly with soap and water
- *If you do become ill, stay off work or school until at least 48 hours after the symptoms have passed
- *Disinfect any surfaces or objects that could be contaminated
- *Wash any items of clothing or bedding that could have become contaminated separately on a hot wash
- *Do not share towels and flannels
- *Ensure toilets and the surrounding areas are cleaned thoroughly
- *Avoid eating raw, unwashed food produce
Prof Martin Marshall, from the Royal College of GPs, said: "This study makes clear that as we've seen with other contagious diseases, such as colds and flu, prevalence of gastro-intestinal infection was lower during the pandemic. This is likely to be in a large part due to restrictions that were implemented to stop the spread of Covid, and greater adherence to public health measures.
"As we move to the next stages of the pandemic, severe restrictions have been, and continue to be, lifted to allow a more normal way of life, but practising good hygiene measures is something that can and should continue, and really can help people keep well."