Midlanders suffering from a stomach bug are being urged not to go to their GPs, local hospital, work or school by health bosses.
Winter vomiting disease, known also as norovirus, causes sickness and diarrhoea which can last for two to three days, but it is also highly infectious.
A warning issued by Birmingham East and North Primary Care Trust calls for people with these symptoms to stay at home until they are fully recovered.
The virus, which led to two hospitals in Birmingham and Sandwell closing wards, can be caught either through contact with an infected person or by touching contaminated services, like door handles or tables.
Last month City Hospital closed ward D26 following an outbreak, banning visitors and sending ward staff home, while Sand-well General was forced to close Linden 5 and Priory 5 after 40 patients became infected in November.
Outbreaks are more common in enclosed spaces like GP surgery waiting rooms, nurseries, schools, hospitals and care homes.
A spokeswoman for Birmingham East and North PCT said: "A significant number of people living across Birmingham are currently suffering from a stomach bug, causing sickness and diarrhoea.
"There is no specific treatment for Noro-virus, it's best to just let it run its course.
"Don't go to work, school or any other public places. Stay at home for 2-3 days until your symptoms have passed.
"Don't go to hospital. There is no treatment for the bug and you are likely to pass it on to other people who are at hospital for other reasons, possibly making them ill. Similarly, don't visit your GP unless absolutely necessary.
"The best way to get health advice is to call NHS Direct on 0845 46 47."
Other tips to aid recovery include washing hands after going to the toilet or preparing food, as this can stop the virus from spreading or picking up the bug in the first place.
Avoid preparing food for others until at least three days after your symptoms have gone, and if you have symptoms avoid direct contact with others for at least 48 hours.