A surge in parasite-linked illnesses has health officials across the United States on alert.

Cyclosporiasis, caused by the parasite cyclospora, has made headlines this summer, as investigators work to identify its source.

"It is a microscopic parasite. So, you can't see it with the naked eye," says Sharjeel Ahmad, MD, an infectious disease doctor with OSF HealthCare. "It causes an infection of the small intestine and produces a diarrheal illness."

As of July 14, nearly 7,000 cases of cyclosporiasis across 34 states are under investigation, with 141 people hospitalized, according to the U.S. Centers for Disease Control and Prevention (CDC). “This is substantially higher than the 249 cases reported nationally by this same time last year,” the CDC points out.

Michigan has reported the most cases so far, with health officials there recently identifying lettuce as a possible source.

How does cyclospora spread?

Unlike other gastrointestinal illnesses like norovirus, cyclosporiasis does not spread from person to person. Instead, the parasite must mature in the environment before it becomes infectious, a process that can take up to a week, Dr. Ahmad says.

"It's beginning at the farm," Dr. Ahmad says, adding that it spreads through fecal matter contaminating the soil and water, which then passes on to the food being grown.

Common foods affected are leafy greens like lettuce, as well as herbs, melons and berries.

"When the running water for irrigation gets contaminated, then the soil gets contaminated while you're growing raw produce," Dr. Ahmad adds. "It's meant to be consumed raw, but things like berries and lettuce have a big surface area with crinkles, cracks and crevices."

Contamination can also occur during harvesting if workers do not properly wash their hands after using the restroom.

How to reduce your risk

Wash each piece of produce individually.

"Washing may not make the risk go down to zero, but that's your best bet. Wash your hands first before you wash the products and then wash them individually," Dr. Ahmad says. "That will give you the most effective protection. Take the berries individually and washing them will help more than anything."

Refrigerating or freezing the products does not kill the parasite. Only cooking produce to 158 degrees Fahrenheit or hotter can kill it. Chemical washes and vinegar are not guaranteed to eliminate the parasite. Don’t use bleaches or other cleaners with your food, as they can cause health problems.

People who are pregnant or immunocompromised should be especially cautious, Dr. Ahmad says. During this time, Dr. Ahmad recommends that such people only eat leafy greens after they have been thoroughly cooked.

Cyclosporiasis symptoms to look out for

While explosive diarrhea has received the most attention, it is not the only symptom of cyclosporiasis. Other symptoms include:

• Bloating
• Cramping
• Fatigue
• Loss of appetite
• Low-grade fever
• Headaches
• Weight loss

Symptoms may come and go, meaning you may feel better for a period before they return, and they can last anywhere from a few days to a month.

Treatment options currently available

Treatment includes staying hydrated by drinking plenty of fluids and replacing lost electrolytes. An antibiotic called Bactrim, the brand name for trimethoprim-sulfamethoxazole, can be prescribed to kill the parasite and relieve symptoms.

Healthy adults may eventually clear the infection on their own as the immune system fights off the parasite. However, if your symptoms are severe, Dr. Ahmad recommends contacting your primary care provider to discuss testing. Routine stool tests do not screen for cyclospora, so a specialized test must be ordered.

Dr. Ahmad expects cases to continue increasing over the next few weeks before gradually declining. Historically, most cyclospora infections are reported between May and August, but this year is a much bigger outbreak than usual.

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