An outbreak of the highly infectious norovirus affected a part of the geriatric ward of the East Limburg Hospital (ZOL) on Sunday evening.
As a result, the department was placed under quarantine, said the institution's spokesman.
"The situation is now fully under control with the help of nurses, doctors and the hospital hygiene department. The virus, therefore, remains confined to a single department," said ZOL spokesman Jurgen Ritzen.
Stringent hygiene rules have been applied - such as extensive and repeated hand-washing - to prevent the spread of the virus.
People outside the hospital who may have symptoms of the disease are asked to stay at home. The first symptom is often sudden nausea, followed by vomiting and diarrhoea. Some people may also experience a mild fever, headache, stomach cramps and aching limbs.
Noroviruses are extremely contagious and spread easily from person to person in a number of ways. People can become infected through eating food or drinking liquids contaminated by infected food handlers, touching surfaces or objects contaminated with norovirus and then touching their mouth before hand washing, or having direct contact with another person who is infected and then touching their mouth before hand washing.
The Brussels Times