Nosocomial Transmission of M tuberculosis From an Extrapulmonary Site
Abstract & Commentary
Synopsis: The surgical wound in a patient treated for tuberculosis orchitis appeared to have been the source of infection of health care workers.
Source: D’Agata EM, et al. Nosocomial transmission of Mycobacterium tuberculosis from an extrapulmonary site. Infect Control Hosp Epidemiol. 2001;22:10-12.
A 71-year-old man was admitted to a community hospital with a 2-week history of fever and an indurated, tender right testicle. He had no respiratory symptoms, and an admission chest x-ray was normal. Blood and urine cultures were without growth. He was given broad spectrum antibiotics, but his symptoms worsened. He underwent a right orchiectomy; bacterial cultures of operative material were without growth. He was admitted to the intensive care unit without respiratory precautions. The wound was packed and irrigated twice daily. Because of persistent fever and onset of tenderness in the left testicle he was taken to the OR on the 12th hospital day for a left orchiectomy and drainage of a prostatic abscess. Bacterial cultures were again negative, and the previous regimen of wound packing and irrigation were continued. He subsequently had a downhill course with deteriorating mental status and respiratory failure requiring intubation. Chest x-rays showed a pattern compatible with pulmonary edema; bronchial washings were negative for bacteria and acid-fast bacilli (AFB). A CT scan of the head showed multiple ring-enhancing lesions. The patient expired on the 27th hospital day. At autopsy, he was found to have caseating granulomata with AFB in multiple tissues; cultures grew Mycobacterium tuberculosis.
A contact investigation of exposed healthcare workers was undertaken. The ICU had 6 air exchanges per hour. The autopsy room had 12 air exchanges per hour with air exhausted to the outside; the autopsy personnel wore surgical masks. The hospital has an active tuberculin skin test (TST) program. In the preceding year, the conversion rate was 0.14% (2/1435 employees). Of the employees exposed, 12/95 (13%) converted. All of 3 autopsy personnel and 6 of 28 nurses (21%) converted. In addition, 2 of 17 respiratory therapists and 1 of 12 members of the surgical team converted. Among the nurses, the only independent risk factor associated with conversion was packing or irrigation of the wound (odds ratio [OR] 95%; CI, 1.2-67).
Comment by Robert Muder, MD
Transmission of tuberculosis is by the airborne route; a patient with pulmonary or laryngeal tuberculosis is nearly always the source. Transmission of tuberculosis from an extrapulmonary site is unusual, since generation of an aerosol is required. However, aerosols can be created from wounds under certain circumstances. In a previously reported outbreak, 9 secondary cases of TB and 59 conversions occurred after exposure to a patient with a large tuberculous abscess of the hip.1 Irrigation of the wound with a Water Pik dental appliance appears to have contributed to the outbreak, as did positive pressure ventilation in the patient’s room.
In the report by D’Agata and colleagues, several factors mitigate against a pulmonary source of transmission. The patient had a negative chest x-ray on admission, and bronchial washings were negative for AFB. There was a strong association between wound irrigation and skin test conversion. Finally, all of the autopsy personnel converted.
This case has several important lessons for control of tuberculosis in the hospital. The first is that tuberculosis is often unsuspected on presentation. In retrospect, TB was a prime consideration for the etiology of refractory epididymoorchitis in an elderly man whose bacterial cultures were negative, and who failed to respond to antibacterial therapy. The second is that TB can be transmitted from an extrapulmonary source if the organism load is large and the site of infection is disturbed in such a way as to create potential aerosols during debridement or irrigation. Patients with open lesions due to M tuberculosis should be placed in isolation, with 12 air exchanges per hour and air exhausted to the outside, until the site is sterilized by appropriate therapy.
Finally, the case points out the inadequacy of standard surgical masks for protection of health care personnel. Infective droplet nuclei are approximately 1-5 microns in size. Paper surgical masks are meant to protect surgical patients from the nasal exhalations of surgical personnel; they do not filter micron-sized particles. Approved health care particulate respirators are needed to protect personnel from infectious aerosols.
Reference
1. Hutton MD, et al. Nosocomial transmission of tuberculosis associated with a draining abscess. J Infect Dis. 1990;161:286-295.
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