Traces of nickel and lead have been found in blood samples taken from hundreds of patients in hospital with a mysterious illness in India.
The Andhra Pradesh state government said investigations by experts from the All India Institute of Medical Sciences has not been able to ascertain the possible source of excessive nickel and lead particulate matter in the patients' blood.
Reports from other tests by experts at the Indian Institute of Chemical Technology, including toxicology reports and blood cultures, are being awaited, the statement said.
Health officials and experts are still baffled by how the heavy metals got into the patients' blood, and whether it is the cause of the mysterious illness that has left 585 people in hospital and one person dead in Andhra Pradesh.
The illness was first detected on Saturday evening in the ancient city of Eluru.
People with the disease started convulsing without any warning, said Geeta Prasadini, a state health official.
Andhra Pradesh chief minister YS Jaganmohan Reddy held a virtual meeting on Wednesday with officials who included experts from India's top scientific institutes. Mr Reddy said 502 people with the illness were discharged after showing improvement.
The patients showed symptoms ranging from nausea and anxiety to loss of consciousness.
What is confounding experts is that there does not seem to be any common link among the hundreds of people who have fallen sick. All of the patients have tested negative for coronavirus and other viral diseases such as dengue, chikungunya and herpes.
The patients are not related to each other and do not all live in the same area. They are from different age groups, including about 70 children, but very few are elderly.
Initially, contaminated water was suspected. But the chief minister's office confirmed that people who do not use the municipal water supply have also fallen ill, and that initial tests of water samples did not reveal any harmful chemicals.
A 45-year-old man who goes by the single name Sridhar was hospitalised with symptoms resembling epilepsy and died on Sunday evening, doctors said. His post-mortem did not shed any light on the cause of death.
Andhra Pradesh state is among those worst-hit by coronavirus, with more than 800,000 detected cases. The health system in the state, like the rest of India, has been frayed by the virus.