A highly drug-resistant strain of typhoid is spreading in Pakistan, killing four and affecting around 850 others.

The “extensively drug-resistant” bug was first identified in November 2016 in Hyderabad but has since spread to other parts of the country. According to the Pakistani National Institute of Health Islamabad four people have died and 858 people have become infected with the resistant strain of the disease.

Because typhoid spreads quickly via food and water – and in places where there is poor sanitation – doctors are worried about the drug-resistant bug's potential to threaten vast numbers of people in Pakistan and beyond.

In December, the strain was identified in a patient who came to the UK from Pakistan. The patient, who was isolated and treated successfully, was one of around 300 diagnosed with typhoid in the UK every year, the majority of whom are infected in India, Pakistan and Bangladesh.

Antibiotic resistance is a growing problem in lower and middle-income countries such as Pakistan and India, where drugs are poorly regulated and it is easy to buy antibiotics over the counter. There have also been reports of superbugs in countries such as Yemen and Syria, where the health infrastructure has been damaged after years of unrest.