You may have put it down to the turkey leftovers, a dodgy prawn, or too much Christmas cheer.
But if you got gastro towards the end of last year, as hundreds of West Australians did, it may not have been your food that was the problem.
The number of viral gastro cases in Perth exploded in 2021, with 544 recorded rotavirus infections in the metro area, compared to 175 the year before.
But Simon Torvaldson, the group chair of the WA branch of the Australian Medical Association, said the actual number of cases was likely much higher.
"A lot of people with milder gastro will simply tough it out without seeing a doctor," he told ABC Radio Perth's Christine Layton.
"And to be honest, other than helping you with the symptoms and making sure you stay as hydrated as possible, there is little that doctors can do."
Sicker second half of the year
Although the overall number of gastroenteritis cases, including those from food contamination, was within the normal range, the spread of rotavirus spiked dramatically in the second half of last year.
A total of 163 rotavirus cases were recorded in November, compared to 18 for the same month in 2020.
The five-year average sits at 28.4 cases for that month.
Outbreaks also dampened the festive season for many, doubling over the Christmas and New Year period compared with the previous year.
There were 16 recorded outbreaks between December 20 and January 2, compared to seven the year before.
"It indicates a typical viral gastro outbreak where you can see over a period of a couple of months or so there was a sudden spike in cases," Dr Torvaldson said.
Unlike other forms of gastroenteritis caused by food contamination, rotavirus spreads through direct or indirect contact with an infected person's stool.
About 75 per cent of reported cases came from childcare centres.
"In this case, it was rotavirus that was the main culprit and that principally does affect younger people, although adults can get it as well," Dr Torvaldson said.
He said most children were vaccinated against rotavirus when they were babies.
WA Health said it had sent an alert to childcare centres in response to the outbreaks over Christmas and New Year.
Its figures showed that, of all the gastro cases recorded during Christmas and New Year, 55 per cent were 'campylobacter' infections.
These are commonly caused by consuming contaminated, raw or undercooked poultry, meat, or eggs.
Rotavirus accounted for 18 per cent of cases.
A further 16 per cent were caused by salmonella.
Reducing the spread
WA Health said handwashing was the key to preventing the spread of gastroenteritis particularly after going to the toilet, before eating, and after changing nappies.
It said children who were unwell should stay at home for 48 hours after their symptoms ended.
Germs could be shed in faeces for up to a week after symptoms ended, so people were urged to be extra careful with handwashing and cleaning during this time.
WA Health also urged parents to ensure their child's immunisation was up to date.
Babies should be immunised at two, four and six months of age.
