Sources from the Centers for Disease Control and Prevention told CNN on Thursday that seven CDC staffers that were sent to investigate the health impacts of a toxic spill that resulted from a Norfolk train derailment in East Palestine, Ohio, on February 3rd, have fallen ill. 

The source said that all of the investigators experienced similar symptoms, ranging from headaches to sore throats, nausea, and coughing - symptoms similar to those of affected residents nearby.

"Symptoms resolved for most team members later the same afternoon, and everyone resumed work on survey data collection within 24 hours. Impacted team members have not reported ongoing health effects," a CDC spokesperson said in the statement.

The spokesperson noted that the eight other investigators had not reported any symptoms all along. 

The team that reported experiencing symptoms is from the CDC’s Agency for Toxic Substances and Disease Registry, or ATSDR, a branch that assesses the health impacts of chemical exposures. Following the incident on February 3rd, the agency sent 15 investigators to East Palestine to conduct an Assessment of Chemical Exposure, known as an ACE investigation.

Better as soon as they left

A CDC source who requested anonymity told CNN that all seven staffers who reported similar symptoms found it suspicious that they became ill at the same time. However, the source noted that it is still unclear if the chemicals were the cause of it, as fatigue was not ruled out among other possible causes. 

As soon as they had left the area, the investigators reported that they had recovered quickly and later returned to continue their house-to-house survey. Due to this, the incident was not disclosed to the public, the source said, noting that reports of illnesses experienced by CDC staffers wouldn't usually be disclosed. 

"It adds confirmation that the symptoms reported by East Palestine residents are real and are associated with environmental exposures from the derailment and chemical fire," David Michaels, an epidemiologist and professor at the George Washington University School of Public Health, told CNN.

Andrew Whelton, a professor of civil and environmental engineering at Purdue University who has been traveling to East Palestine to conduct independent testing for the town, told CNN, "I think it is important for not only government officials to communicate with each other, but also to communicate their experiences with the public, so that everybody can understand what’s going on, and how help needs to be brought to East Palestine and the surrounding areas."

Read more: Ohio residents diagnosed with bronchitis from chemical exposure

Suing for damages

The disastrous Norfolk train derailment, which resulted in the contamination of air, soil and water in the area was reported as non-hazardous to human health by the Environmental Protection Agency (EPA). 

But residents who continued to report symptoms are doubtful of the agency.

Early survey results from the Ohio Department of Health revealed that 74% of the 514 residents surveyed reported headaches, 61% reported anxiety, 53% reported fatigue and coughing, 50% reported irritation and burning of the skin, and 50% reported sinus congestion.

The train derailment in East Palestine spilled more than one million gallons of hazardous chemicals, recklessly endangering residents and violating a total of 58 federal and state laws.

On March 5, local authorities reported that another Norfolk Southern train derailed in the US state of Ohio, and citizens have been told to avoid the accident site.

On March 15, the state of Ohio sued Norfolk Southern to ensure that the railway pays for all cleaning expenses and damages related to the toxic chemicals spilled during the derailment. 

"Ohio shouldn't have to bear the tremendous financial burden of Norfolk Southern's glaring negligence," Ohio Attorney General Dave Yost said after filing the lawsuit.

Through the lawsuit, the State is seeking civil penalties and other economic losses from the incident. 

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