The nationwide outbreak of cyclospora is likely due to sewage contamination infiltrating the food supply, according to scientific researchers and public health officials. This parasite tends to spread in a cyclical manner.
What is Cyclospora?
Cyclospora is a single-celled protozoan that exists only in humans. It replicates within the intestinal tract, causing severe diarrhea. The organism reproduces by releasing oocysts, which are excreted in human feces.
Contamination Pathways
In the United States, feces typically enter sewage systems. In some states, sewage water is treated, although this treatment is not always effective in removing or killing cyclospora oocysts. Treated water is then released into waterways and used to irrigate crops.
With warm temperatures, these oocysts mature in about a week. A person consuming irrigated food or contaminated water may become sick, thereby continuing the cycle of contamination.
Historical Insight
A public health water microbiologist recounts studying cyclospora during its first documented outbreak in the U.S. in 1995. This small outbreak was originally linked to strawberries grown in California, although the true source was contaminated raspberries from Guatemala. Larger outbreaks followed in 1996 and 1997.
Despite over three decades of study, limited knowledge exists about cyclospora.
Treatment and Surveillance
Using treated sewage for crop irrigation is common. The reasons for collecting and monitoring sewage include assessing community disease levels and evaluating sewage treatment effectiveness against pathogens.
Modern techniques still struggle to detect low levels of cyclospora oocysts, which can nonetheless cause disease.
Global Findings
Worldwide studies indicate the presence of cyclospora oocysts in up to 25% of sewage samples. Concentration levels vary, making it difficult to measure their prevalence.
Infected individuals can excrete between 100 and 10,000 oocysts per gram of feces for up to 60 days. Estimates suggest anywhere from 1 to 100 oocysts per liter in sewage. Improved detection methods are under development.
Sewage Treatment Efficacy
Research on similar protozoa, Cryptosporidium and Giardia, shows partial success in sewage treatment. Chlorine treatment can eliminate high percentages but not all protozoa, leaving some capable of causing disease.
It’s assumed some cyclospora oocysts survive treatment, and thus re-enter the environment, remaining viable for months.
Reuse and Regulations
Annually, 200 billion gallons of treated sewage are used for agricultural irrigation. Treatment varies but often includes additional filtration and disinfection. Unfortunately, regulations addressing protozoa removal in treated sewage are limited.
Effective filtration and ultraviolet light treatments can eliminate protozoa, though chlorine is ineffective against cyclospora.
Risk Assessment
Routine floods and droughts increase the risk of diseases spreading from sewage-contaminated water. Rising temperatures could accelerate oocyst maturation, affecting more people.
Advancements in monitoring and pathogen detection technology are crucial. Expanding wastewater monitoring can mitigate future outbreaks.
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