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

It may be difficult to discern the difference from symptoms alone

PUBLISHED : Saturday, 13 January, 2018, 10:19am
UPDATED : Saturday, 13 January, 2018, 10:19am

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.

“So the doctor will still have to depend on symptoms to decide whether you need antibiotics or not,” he adds. Viral infections cannot be treated with antibiotics.

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Bacteria are single-celled organisms which can survive under a variety of conditions. Most do not cause harm to people in small numbers – for example, many varieties of bacteria living in your gut can even be beneficial. Common bacterial infections include tuberculosis, strep throat and urinary tract infections.

Unlike bacteria, viruses are not living organisms but attach themselves to live host cells in order to survive and multiply. All viruses are harmful to human health. They are responsible for illnesses such as the common cold, chickenpox and Aids.

“Viral infections can be as precarious as bacterial infections,” Choi says, adding that more than 400 people die from influenza each year in Hong Kong.

Ultimately, Choi insists that it is the severity of the patient’s symptoms which should make them decide whether to see a doctor.

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“It’s not whether this is a viral or bacterial infection – the agent itself is irrelevant,” he says.

“The clinical feature is the most important part, and the doctor will make the decision after a physical examination as to the nature of the illness, then diagnose it and prescribe proper treatment.”