A mysterious illness has sickened hundreds of people in a city in southeastern India, according to news reports. Over the weekend, more than 300 people in the city of Eluru, located in the state of Andhra Pradesh, were hospitalized with epilepsy-like symptoms, including seizures and loss of consciousness, as well as nausea and vomiting, according to CNN.

One patient with these symptoms died from a cardiac arrest, but officials said the death appeared unrelated to the mystery illness.

Although coronavirus infection is widespread in the area, all of these patients tested negative for COVID-19, according to CNN.

In addition, blood tests performed so far have not found evidence of other viral infections, such as dengue fever or chikungunya, CNN reported.

By Monday, about 180 patients were well enough to be released from the hospital.

Officials were looking into a number of possible cultripts for the illness. Initially, officials suspected water contamination, because all the patients were found to have a common water source, CNN reported.

However, Andhra Pradesh's state Health Minister Alla Kali Krishna Srinivas said that tests had ruled out water contamination as well as air pollution as the cause of the mystery illness, CBS News reported.

Officials were still conducting blood tests for pathogens such as E. Coli. (Infections with E. coli can cause nausea and vomiting, but not typically seizures.)

Authorities from a number of leading Indian health institutes, including the All India Institute of Medical Sciences in New Delhi, are heading to Eluru to help investigate the cases, according to CBS News.