Diarrhoea and vomiting can be of both infectious and non-infectious origin. By looking at the symptoms you can often get an indication of what caused them, but an exact diagnosis calls for additional examinations. Bacteria, viruses and parasites can all cause stomach infections.

Virus infections are most common among children and most cases occur in autumn, winter and spring. Bacterial infections peak summer and autumn. Parasite infections are rarer than virus or bacterial infections.

You have to eat bacteria or parasites to become ill. Most of these infections are therefore transmitted via food, but the micro organisms can also be found in contaminated drinking water. A person secreting multiple micro organisms can indirectly transfer the infection by contaminating food meant for others, or more rarely by direct contact.

Virus primarily spread from person to person, but can also spread via food contaminated with virus from a contagious person. The incubation period for stomach infections is between 12 hours up to one week.

A simple stomach infection is indicated by general discomfort, stomach aches and rumbling, nausea, vomiting, diarrhoea and sometimes fever. The different symptoms can be present in varying degree. A short course of illness lasting a few days, dominated by vomiting indicates a virus infection. Bacterial and parasite infections - more dominated by diarrhoea - often have a longer course, bacteria about a week, parasites somewhat longer.

However, the course of the different infections vary to such a degree that you cannot say anything definite about the cause of the disease based on the symptoms alone. Up to 25 percent of all people experiencing a stomach infection will still have problems 6 months after the acute infection. Symptoms can be continuing loose stools, recurring diarrhoea, constipation, stomach aches and rumbling. The cause of these problems is unknown.

Source:

Peter Gerner Schmidt, Dr. Med, Blenda Böttinger, Dr. Med, Eskild Petersen, Consultant Doctor, "Lægernes patientvejledning 2003", page 28.