A contaminated endoscope that may have transmitted tuberculosis (TB) between two hospital patients has highlighted the need for scrupulous adherence to endoscope cleaning procedures and the value of maintaining TB DNA fingerprint registries.
The discovery was made when researchers from the Johns Hopkins School of Public Health, the School of Medicine, and the Maryland State Department of Health and Mental Hygiene found identical DNA "fingerprints" in bacterial cultures isolated from two TB patients. Since the TB cases were detected six months apart, a link between the two people was unsuspected until DNA fingerprinting revealed a perfect match. The only identifiable link between the two patients was the hospital where they both had been bronchoscoped. A study of how the discovery was made appeared in the October 1, 1997 issue of The Journal of the American Medical Association (JAMA).
Senior author William Bishai, MD, PhD, assistant professor, Molecular Microbiology and Immunology, Johns Hopkins School of Public Health said, "Without a DNA fingerprint registry of all TB samples, such as we had in this instance, we would have been unable to confirm a connection between these two cases. Registries can help identify unsuspected modes of TB transmission." DNA fingerprint registries also help estimate the relative frequency of first-time TB infections, distinguish reinfections from relapses, and
An examination of the two patients' records at the hospital in question showed that both patients had been bronchoscoped with the same instrument in the same room. No other bronchoscopies were done between the two patients. The procedures used by the hospital to clean, disinfect, and sterilize bronchoscopes did not conform to national guidelines. Researchers with the study also inspected the locations where TB patients were treated, checked the ventilation and air-filtering systems, and observed the cleansing, disinfection, and sterilization of bronchoscopes. "We made a thorough examination of every possible avenue of contamination before turning to the equipment," said lead author Theresa Michele, MD, fellow, Division of Pulmonary and Critical Care Medicine, Johns Hopkins School of Medicine.
The Association of Practitioners in Infections Control (APIC) recommends that endoscopes be processed between uses by thorough and immediate cleansing with enzymatic cleaner, followed by complete immersion for 45 minutes at 25 degrees centigrade for eradication of bacteria; this is supported by the Food and Drug Administration (FDA). Chlorhexidine gluconate solutions have been shown to inadequately kill the bacterium responsible for TB. The endoscope's suction valve and tubing is particularly difficult to clean. Many centers now use disposable suction tubing and all removable parts and accessories that can withstand heat are steam-sterilized.
This study was supported in part by grants from the National Institute of Allergy and Infectious Diseases (NIAID), the National Institute on Drug Abuse (NIDA); and the Centers for Disease Control and Prevention (CDC).
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