False-positive Results of Campylobacter Rapid Antigen Testing

To the Editors: We report 2 infants in whom a potentially false-positive rapid Campylobacter antigen test occurred in the setting of a confirmed unrelated diagnosis. Case 1: A 5-month-old boy presented with a history of chocolate-colored diarrheal stools, vomiting and irritability, and a palpable mass in his upper abdomen noted by his mother. Three days into the course, he was evaluated by his pediatrician. Stool tested positive for occult blood, a catheter urine specimen was obtained, and intramuscular ceftriaxone was given. The following day, he was admitted to the local hospital for intravenous hydration and further evaluation. C-reactive protein elevated at 5 mg/dL and a normal complete blood count, electrolytes, and transaminases were noted. Fecal leukocytes were reported and rapid antigen testing for Campylobacter sp with the immunoCard STAT!CAMPY (ICS CAMPY) (Meridian Bioscience Inc., Cincinnati, OH) test kit was positive. Routine stool culture was obtained at this time was negative for bacterial stool pathogens. Clostridium difficile toxin assay was negative. Abdominal radiographs showed a possible bowel obstruction, and a repeat film the following morning revealed small bowel obstruction, prompting transfer to our institution. Shortly after arrival, the patient underwent air enema which demonstrated intussusception that was complicated by subsequent bowel perforation. The infant underwent resection of his cecum, ascending colon, and transverse colon with a primary anastomosis of the proximal portion of his descending colon. Azithromycin and meropenem were initiated following surgery, and a stool specimen was obtained after the first dose. The stool sample was placed in Cary-Blair transport media (Remel Inc., Lenexa, KS) and plated on cefoperazone-vancomycin-amphotericin B sheep blood agar (Remel, Inc. Lenexa, KS) specific for Campylobacter isolation. Following incubation at 42°C under microaerophilic condition for 3 days, the stool culture was reported as negative for Campylobacter sp. The patient was discharged home on postoperative day 5 and has continued to do well at follow-up 4 months later. Case 2: A 9-month-old had 5 days of high spiking fever, conjunctivitis, mucositis, rash, and swollen hands and feet. She was admitted to a community hospital and treated with intravenous ceftriaxone after elevated white blood cell count, and inflammatory markers were noted. Blood and urine cultures were negative. She had sudden deterioration with development of seizures and shock on day 7 and was transferred to a regional hospital. There the infant required intubation, ventilation, and vasopressors. Additional work up included negative blood culture. Because of a history of loose stools, ICS CAMPY was performed and reported as positive. Concurrent culture for Salmonella and Shigella was negative, but the sample was not tested for Campylobacter. She improved and was discharged back to her primary pediatrician after a 7-day stay. Two weeks into the course of fever, her primary pediatrician suspected the diagnosis of Kawasaki disease and the infant was referred to our institution. Peripheral desquamation, continued marked C-reactive protein elevation, and thrombocytosis were noted. Although echocardiogram performed days before was normal; current echocardiogram demonstrated extensive coronary ectasia. She had a good clinical response to IVIG and infliximab therapy. Data from the Minnesota Department of Public Health (presented at 2009 OutbreakNet) revealed that when ICS CAMPY STAT! was used, only 55% of initial positive results were repeat positive and only 14% were positive by culture. Many of the false-positive specimens came from children with bloody diarrhea leading to speculation regarding the possible effect of blood in the stool on test performance. We wish to alert clinicians to the increase in routine use of Campylobacter rapid antigen testing by many laboratories, and the potential for false-positive results.1,2 For now, we suggest caution in interpreting rapid ICS CAMPY tests and that back-up culture should be used in all cases of positives. Further research into the performance of the test particularly in those with bloody stools is warranted. Angela L. Myers, MD, MPH Mary Anne Jackson, MD Department of Pediatrics & Section of Infectious Diseases Children's Mercy Hospitals & Clinics The University of Missouri-Kansas City [email protected]