Viruses vs bacterial infections: how can you tell the difference?

Have you ever been laid up in bed for days with a headache, sore throat, runny nose and bad cough that won’t go away? These symptoms are all too familiar and common, but how do you know if they are caused by bacteria or a viral infection?

Both viruses and bacteria are passed on by contact with infected people, touching contaminated food, surfaces and water, and through coughing and sneezing.

Many symptoms of illness, such as diarrhoea, vomiting and inflammation, can be caused by viruses and bacteria. However, it may be difficult to tell the difference between the two from symptoms alone.

“If you have a cough or cold and the colour of the sputum and nasal discharge is clear or whitish, this is more likely to be an upper respiratory tract infection of which 90 per cent are caused by viruses,” says Dr Gabriel Choi Kin, president of the Hong Kong Medical Association.

“The other 10 per cent of upper respiratory tract infections can be due to bacteria. So a clinical decision alone may not be adequate – sometimes you may need a culture of the sputum to be more certain if your illness is caused by a virus or bacteria.”

Choi advises that a definitive lab culture result takes four days, by which time a viral infection may have already passed, or a bacterial infection may become much more serious.