DETROIT — The number of cyclosporiasis cases reported in Michigan since the outbreak began in late June rose to 9,253 on Monday, a 13% increase over Friday's total.

Health officials continue to investigate the state's worst-ever outbreak of the parasitic illness, which usually only affects around 50 people each year. As of Thursday, 160 people had reportedly been hospitalized, according to the Michigan Department of Health and Human Services.

The department reported 1,077 new cases on Monday, but 475 of those cases were not previously reported due to delayed lab testing, according to a note on the MDHHS website. The number of cases of cyclosporiasis reported each day hit a peak on July 13, with 726 cases.

Cases had been reported in 70 of Michigan's 82 counties as of Thursday, according to the state health department. The largest numbers were in Wayne County with 1,036 cases, Washtenaw County with 773, Oakland County with 710 and Ingham County with 698.

Dr. Teena Chopra, professor of internal medicine in the Division of Infectious Diseases at Wayne State University School of Medicine, said the epidemic curve seems to "plateau." But people can't say cases are decreasing, she said, because of reporting delays and the fact the disease has a prolonged incubation period.

MDHHS has said the time between being exposed and becoming sick is usually about a week but can range from two days to more than two weeks.

Chopra said it's important to not "over-interpret" the data.

"But overall, the curve seems to flatten a bit and hopefully it should go on a downward slope in the next few weeks," she said in an email.

Outbreak spreads across U.S.

The Centers for Disease Control and Prevention has linked the outbreak to four additional states, tracing the outbreak to shredded iceberg lettuce from central Mexico, according to The Washington Post, which spoke to two individuals familiar with the CDC investigation.

So far the outbreak has been linked to Michigan, Indiana, Kentucky, Ohio, West Virginia, Kansas, Illinois, Oklahoma and Pennsylvania.

Chopra said last week that the size of the outbreak is "unprecedented."

"We haven't seen it before," she said, referring to the U.S. "We do see cases every year, but not this magnitude. So this is definitely way beyond the numbers we've ever seen before."

Chopra said that water contaminated with human stool being used to irrigate produce is likely the cause of the outbreak.

California-based Taylor Fresh Foods voluntarily recalled all iceberg lettuce grown in central Mexico that was identified as the potential source of the Cyclospora outbreak, the company said in a previous statement.

MDHHS spokesperson Lynn Sutfin said the department can't say for certain if cases in Michigan have peaked and will start declining.

"But should the recall be effective in removing contaminated product from circulation, we are likely to start to see case reports stabilizing and even decreasing in the following weeks," she said.

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