Viral or bacterial?

Dr Subramanian Swaminathan writes about how one can differentiate between viral and bacterial infection.

The news about antibiotic resistance and “superbugs” has become a daily affair now, with doctors repeatedly warning the public to avoid antibiotics for viral infections. How does one know the difference between the two? Viral infections are manifold, and the presentation varies based on various factors, including the patient’s immune system. Most viral infections are short-duration, but some like HIV and Hepatitis B are long-term; most are self-limiting like the common cold, but some like Ebola are often fatal. Most cause infection once in a lifetime like hepatitis A, but some like influenza can cause repeated infections. Therefore, “viral infections” in the medical sense are too broad a term to define. On average, most infections in the community are caused by viruses, many more folds than bacteria.

In colloquial parlance, viral infections refer to self-limiting communicable infections like respiratory viruses (influenza, SARS-CoV-2, etc.), mosquito-borne (dengue, chikungunya, etc.), or diarrhoeal infections (rotavirus, norovirus, etc.). These cause short-duration illness with fever, mild chills but not shivers, significant body aches, and tend to resolve within 4-5 days. Bacterial infections often cause fever with shivers and tend to last longer. At the beginning of an illness, it may be difficult to differentiate a viral from a bacterial illness, but the differences become apparent in a few days. Some infections (like urinary infections) are almost always caused by bacterial pathogens, and infections like upper respiratory infections are overwhelmingly caused by viral pathogens although bacteria may rarely do so.

With respiratory or diarrhoeal viral illnesses, there are usually others around the patient in the same family who may have similar symptoms — this is quite unusual in bacterial infections. This history of “sick contacts” is an important detail that is often sought in history taking. Untreated bacterial infections can get worse, but patients with viral infections often feel significantly better with simple measures like hydration, fever control, decongestion, and other such measures.

Some viral infections do have specific antiviral treatment (like oseltamivir for influenza) but for most, it is based on symptoms. Bacterial infections like urinary infections require specific antibiotics based on guidelines. Unfortunately, while these are differences in general, there is considerable overlap between the two syndromes, and fever should be interpreted by a medical professional.

(The author is the director of infectious diseases at a leading hospital in Bengaluru.)