The case of the two ill workers at an unidentified Indiana pig slaughterhouse is being investigated by federal officials who wish to verify whether there is a link with another similar outbreak reported at a slaughterhouse in Minnesota.

Workers at a pork plant in Indiana presented symptoms which were found to be similar with those in slaughterhouse workers from Austin, Minnesota, who had complained of bad health last month.

The Centers for Disease Control and Prevention are investigating whether there is a link between the two cases. One common characteristic which ignited the agency’s intervention is that all the employees work in areas where a specific procedure is used to remove the brains out of pigs’ heads, CDC spokeswoman Lola Russell told the Associated Press.

The animals’ heads are processed using a technique in which compressed air is shot into their skulls to forcibly remove the brains.

After the Minnesota slaughterhouse illness was reported, the CDC began its investigation by looking at slaughtering practices in 25 large pork processing plants in 13 states, the AP reports.

The above-mentioned technique was found only in one Indiana plant and one Nebraska plant.

Minnesota health officials said the pork plants in all three states have voluntarily stopped the practice.

An initial suspicion in the Minnesota illnesses was that the workers had come in contact with the pigs’ brains, thus becoming infected with something. No viruses or bacteria have been identified so far though, according to officials. No chemical toxins were involved either.

The investigation continues as some of the 12 workers from Minnesota are still being treated, though their illness remains a mystery.

The discovery of the Indiana illness and its ongoing investigation “may help us figure out why these workers are getting sick,” Minnesota state epidemiologist Ruth Lynfield was quoted as saying by the AP.

The name or location of the Indiana plant has not been disclosed in an effort to maintain privacy. The ill workers’ symptoms included changes in sensation and weakness in their limbs. The Indianapolis Star adds that the two workers’ condition is not life-threatening.