NEW DELHI — India’s confirmed coronavirus cases and deaths remained below record levels in the last 24 hours, but authorities are worried about fungal infection that attacks those with weak immune systems.

Doctors suspect that the sudden surge in mucormycosis, or “black fungus” infection, may be linked to the use of steroids to treat COVID-19. It can result in breathing problems and coughing blood.

India reported 4,209 COVID-19 fatalities in the past 24 hours and 259,591 new confirmed cases. Experts believe both figures are an undercount.

Megacities such as Mumbai and New Delhi have seen signs of improvement in recent days. But there is growing concern about smaller towns and rural areas where the virus has made inroads, stretching the weak health system.