Understanding the Cyclospora Outbreak and Its Connection to Sewage Contamination

The widespread cyclospora outbreak in the U.S. is likely linked to sewage contamination in the food supply. Public health officials and scientists suggest that this parasite’s spread can create a cycle hard to break. Cyclospora is exclusive to humans, where it reproduces in the intestines, causing intense diarrhea.

The organism spreads by releasing oocysts in human feces. In the U.S., these typically enter sewage systems. Some states treat sewage water, but the treatments don’t always eliminate the oocysts. This treated water often ends up in waterways or is used to irrigate crops. In warm environments, the oocysts mature in about a week. People consume the tainted food or water and fall ill, perpetuating the cycle by releasing more oocysts into sewage systems.

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I have been researching cyclospora since the first outbreak in 1995 in Florida, involving 45 cases. Initially, strawberries from California were blamed, but later, contaminated raspberries from Guatemala were suspected. Guatemala’s raspberries were also linked to major outbreaks in subsequent years. Today, more than 30 years later, the U.S. faces its largest outbreak, affecting over 22,000 individuals and resulting in two deaths in Michigan.

Treating sewage for irrigation is common where water resources are scarce. We monitor sewage for pathogens to assess community disease levels and evaluate treatment effectiveness. However, detecting cyclospora oocysts remains challenging.

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Studies show cyclospora oocysts appear in up to 25% of sewage samples worldwide. A person infected might release up to 10,000 oocysts per gram of feces, persisting for up to 60 days. Our lab at Michigan State University is working on better detection methods. This could help track outbreak trends and assist in sewage management.

Standard sewage treatments may not effectively reduce cyclospora oocyst numbers. Previous research on similar protozoa like Cryptosporidium and giardia revealed that while some protozoa were removed, many remained intact in treated water.

The U.S. uses 200 billion gallons of treated sewage for crop irrigation annually. While some undergo additional filtration and disinfection, many do not. States vary in regulating protozoa removal from treated sewage, and common practices such as chlorination aren’t effective against protozoa. Ultraviolet light, however, has shown promise in inactivating related protozoa.

Droughts and floods increase the risk of sewage contamination in water and food supplies. Rising temperatures can hasten cyclospora maturation. Advanced techniques can improve water quality monitoring, pathogen detection, and containment. Expanding wastewater surveillance could curb future outbreaks and disease spread.

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