Government and medical authorities in the southern state of Andhra Pradesh said that more than 200 people were discharged at the weekend and that tests had ruled out Covid-19, the infection caused by the novel coronavirus.

Further serological tests are underway.

“The causes of the outbreak are not known yet,” the state government said in a statement, adding that people in all age groups appeared prone to the infection.

Separately, India’s federal health ministry said on Monday it would send a team of three medical experts to investigate the outbreak, which has infected more than 300 children, it said.

“The children reportedly suffered from dizziness, fainting spells, headache and vomiting,” the ministry said, adding that a door-to-door survey was also underway.

The state health department was alerted to the first case over the weekend following the death of a 45-year-old man, said Geeta Prasadini, a public health director in Andhra Pradesh state.

“We have taken the patients’ blood samples for serological investigation and bacterial investigation to rule out any type of meningitis,” Prasadini told Reuters.

Authorities were investigating water supplies at 20 locations within the city of Eluru where the outbreak was first reported as well as neighbouring areas, she added.

The state of Andhra Pradesh is also among the worst-affected by Covid-19 in the country.

India, which has recorded 9.68 million Covid-19 infections, is just behind the US in the global tally.