I’m a surgeon. I follow infectious disease and public health. This cyclosporiasis made me look up the parasite. I wasn’t familiar with it. I also wanted to dive into how we detect outbreaks. FoodNet and PulseNet are how we detect and track outbreaks.
While FoodNet acts as the “report card” tracking long-term baseline numbers, PulseNet is the active “detective”. It is a national laboratory network, coordinated by the CDC and the Association of Public Health Laboratories (APHL), designed to detect and stop fast-moving foodborne outbreaks in real time.
If FoodNet tells us how many people are getting sick, PulseNet tells us exactly which people are getting sick from the exact same contaminated source.
“DNA Fingerprinting”
Before PulseNet was created in 1996, if a person in Michigan and a person in Ohio both got sick from Salmonella, local doctors treated them as two isolated, unrelated cases. PulseNet changed that by looking at the pathogen’s genetics.
Isolation: A patient submits a stool sample, and a clinical lab isolates the specific foodborne bacteria (like Listeria, Salmonella, or E. coli).
Sequencing: The local or state public health laboratory sequences the bacterial DNA.
Database Comparison: The lab uploads this “DNA fingerprint” to PulseNet’s central national database.
Connecting the Dots: Specialized software constantly scans the database. If five people in different states all upload an identical DNA fingerprint within the same week, PulseNet flags a cluster. Epidemiologists then step in to interview those five patients to find the common food denominator.
The Modern Gold Standard: Whole Genome Sequencing (WGS)
For its first 20-plus years, PulseNet relied on a technology called Pulsed-Field Gel Electrophoresis (PFGE). Think of PFGE like a low-resolution bar code—it was revolutionary for its time, but sometimes different bacterial strains looked vaguely similar.
By 2019, PulseNet fully transitioned all 50 states to Whole Genome Sequencing (WGS).
- Ultra-High Resolution: WGS reads the entire genetic code of the bacteria, line by line. This allows scientists to see single-nucleotide differences.
- Absolute Certainty: If the Cyclospora or Salmonella from a patient perfectly matches the bacteria found on a conveyor belt at a packaging plant, WGS proves they are the same strain beyond a mathematical doubt.
- Extra Data: WGS simultaneously tells scientists if the bacteria carries specific genes making it resistant to certain antibiotics.
Expanding Scope (Recent Updates)
PulseNet celebrated its 30th anniversary by scaling up its target database. While it historically focused on the “big three” (Salmonella, Listeria, and E. coli), PulseNet expanded its cloud-based architecture to routinely track 9 life-threatening pathogens, integrating Vibrio, Yersinia, Clostridium botulinum, and Cronobacter (the bacteria responsible for infant formula recalls) into its active fingerprint-matching network.
So, now we can discuss Cyclosporiasis. I guess the last time I heard of this parasite was in medical school. It is not that common. It is not something that we normally look for in patients with food poisoning.
Currently, we are living through a record-breaking multistate outbreak of cyclosporiasis, an intestinal illness caused by the microscopic parasite Cyclospora cayetanensis. It has already shaped up to be the worst year for reported cyclospora infections in U.S. history.
Federal health officials (FDA and CDC) have officially identified shredded iceberg lettuce imported from central Mexico as a confirmed source for a major cluster of the outbreak.
- The Specific Link: The contaminated lettuce was supplied by Taylor Farms de Mexico and served at Taco Bell locations across five specific states: Indiana, Kentucky, Michigan, Ohio, and West Virginia.
- Current Action: Taylor Farms has initiated a voluntary recall and is removing all iceberg lettuce sourced from central Mexico from the market. Taco Bell has stopped using this supplier.
- Other Potential Sources: Because more than 30 states have reported cases, health officials warn that not every U.S. illness is tied to this single Taco Bell cluster. They are continuing traceback investigations on other fresh produce items. Historically, outbreaks are linked to fresh, raw produce (like berries, basil, cilantro, and leafy greens) irrigated with feces-contaminated water.
- Case Count: The numbers are staggering and rising quickly. While the CDC’s official lab-confirmed count sits at 1,644 cases, state-level data indicates the actual numbers are vastly higher. For context, Michigan alone has reported over 3,300 cases, and Ohio has hundreds more. This massive gap is due to standard reporting and analysis backlogs.
- Geographic Spread: Cases span at least 31 to 34 states, with the absolute epicenter of the surge located in the Great Lakes region (particularly Michigan and Ohio).
- Severity: There have been over 100 hospitalizations due to severe dehydration, but fortunately, zero deaths have been reported.
It is important for us to be smart. Do not eat fresh, unwashed lettuce! If you have symptoms of watery diarrhea, loss of appetite, cramping, or bloating, go to the emergency room. Tell them what you have been eating. Hopefully, we can control this outbreak and prevent more Americans from getting sick.
