Can a mild infection give you the shakes?

A rigor, the symptom which you experienced, can indeed be alarming. But be reassured: as your GP explained, it is only a bout of exaggerated shivering that occurs when you have a high temperature and is a marker for what may be a significant infection.

When an infection takes hold, the inflammation causes various chemicals to be released into the bloodstream. These alter the setting of the natural thermostat in the brain, causing you to feel cold.

The body tries to remedy this drop in temperature by shivering — an involuntary muscle reflex that causes a rise in body heat.

When diagnosing the cause of rigors, doctors look for evidence of an infection — for instance, a respiratory infection, which would also cause a sore throat or cough; or a urinary infection, bladder pain or burning when passing water.

Abdominal symptoms, such as pain, vomiting or an upset bowel may also signal an infection in the colon, such as diverticulitis.

If nothing is immediately apparent, as was the case with you, reaching a conclusion about the cause is more difficult.

Here, the patient’s medical history is important and we need to consider a range of factors, such as past surgery or rheumatic heart disease (when the lining of the heart or the heart valves is damaged by a streptococcal throat infection earlier in life and has now become a source of infection).

Foreign travel and even contact with animals, may be other factors linked to infection. However, it is quite common to come across patients in whom there is no definite reason for the rigor — and, in a man of your age, the urinary tract is often to blame, even without any specific bladder symptoms.

One possible explanation is the gradual enlargement of the prostate in older men that occurs naturally with age. The prostate gland wraps around the exit pipe from the bladder and any increase in its size hinders the flow of liquid. As a result, there is usually a greater volume of residual urine remaining in the bladder after visiting the loo.

This residual liquid is not noticed by the individual, but the bacteria it contains can multiply and cause infection. The first clue of this might be a rising temperature and rigors — even without any other symptoms.

For that reason, even if an initial clinical examination of the throat, chest and abdomen does not reveal the source of infection, a dipstick test of the urine is essential to confirm or exclude that type of infection.

If testing of the urine shows a normal result and the temperature and rigors continue, then more exhaustive investigation is called for, such as blood tests and examination of the heart, lungs and abdomen by imaging with ultrasound or CT scanning, which may reveal an infection or abscess somewhere else in the body.

This time, the antibiotics you took were effective, despite the lack of an exact diagnosis. But if there is another episode, you should be investigated in further detail.