June 1997
ATLANTA — Efforts by state health officials to expand the scope of disease surveillance and diagnostic testing follow in the wake of two false-positive results of cyclosporiasis and cryptosporidiosis reported in Florida and New York, sparking outbreak alerts, according to a report by the Centers for Disease Control and Prevention (CDC).
The Florida outbreak was suspected because of health experts' inability to document patient histories with specific clinical manifestations and the testing laboratory's positive findings for Cyclospora oocysts. The New York investigation was prompted by the atypical demographic characteristics of the patients with cryptospori diosis reported by one private laboratory.
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During the summer of 1995, in response to a confirmed outbreak of Cyclospora among Florida residents, state health officials began surveillance of the organism. All state laboratories began routine testing for Cyclospora cayetanensis in stool specimens. In July, cyclosporiasis was designated a reportable disease in Florida.
Two weeks after the designation, workers at a Miami children's shelter reported a 3-year-old boy with severe diarrhea and abdominal pain; stool specimens obtained from the boy revealed Giardia cysts. Because of previous giardiasis outbreaks at the shelter, county health officials recommended testing the 13 shelter residents who were pre-school classmates or roommates of the young boy.
One state laboratory reported that stool specimens from six of the shelter's children tested positive for Giardia and six tested positive for Cyclospora. The high proportion of specimens positive for Cyclospora prompted the testing of the shelter's 68 staff members and volunteers. Cyclospora oocysts were identified in 86% of the staff, 64% of the children and 45% of the volunteers.
In response to what county health authorities believed to be an outbreak, they closed the shelter to new admissions, restricted the children's outdoor activities and prescribed trimethoprim-sulfamethoxazole for all 25 children.
"This is an organism we did not know existed until the 1970s," said Dolly Katz, MD, epidemic intelligence service officer for the Division of Parasitic Diseases at the CDC, who was involved in the investigation. "Previously, Cyclospora was only contracted by people visiting foreign countries, but now it's required testing in four states."
In mid-September, the Florida state health department was notified about the apparent outbreak and joined the investigation. The local community hospital, which had begun testing for Cyclospora that same year, was contacted for information about laboratory-identified infections in the community from July through September. Questionnaires were administered to shelter staff, volunteers, the older children and the infants' caretakers, and medical records for the children were reviewed.
The state sent the children's stool samples to the CDC in Atlanta and the University of Arizona for verification. Both reported that all the specimens were negative for Cyclospora. The state central laboratory and the University of Arizona reviewed the slides and identified pollen grains and other artifacts similar to Cyclospora oocysts but lacking its initial morphology. The CDC examined 19 other children at the shelter and identified oocysts in only two.
The health department revised the case definition for cyclosporiasis to include confirmation of Cyclospora infection by a reference laboratory. The state central laboratory initiated a training program at all state labs to teach technicians how to identify Cyclospora and Cryptosporidium.
To improve disease reporting and identify exposures, New York City designated cryptosporidiosis a reportable disease in January 1994, with the city's department of health initiating active surveillance the following November. Each of the clinical laboratories are routinely contacted for reports of new cases and each case is investigated by telephone interview or chart review.
Before the reported outbreak, the laboratory in question had used a modified acid-fast technique to test for Cryptosporidium oocysts. Shortly before, the lab had switched to an enzyme-linked immunosorbent assay (ELISA) to test for Cryptosporidium and began reporting an increased number of positive tests — 52 a month from May-September for a total of 281 in six months.
Because of these findings, the city health department in August 1995, initiated a validation study at the lab to correlate the findings. The lab's samples were sent for parallel tests to the New York City Bureau of Laboratories, who performed the ELISA and acid-fast testing. They were also sent to the New York State Wadsworth Center, David Axelrod Institute for Public Health, which performed ELISA and direct immunoflourescence testing and modified acid-fast testing.
Both reference labs reported only one positive result, conflicting with the earlier results.
Based on these findings, all 280 unconfirmed positive ELISA results for Cryptosporidium identified at the first lab were considered false positives. Physicians for these patients were notified that the previously reported results may have been due to laboratory error.
For more information:
- CDC. Outbreaks of pseudo-infection with Cyclospora and Cryptosporidium— Florida and New York City. 1995. MMWR.1997.15:354-58.
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