Journal Reviews

Undiagnosed TB patient source of insidious spread

D’Agata EMC, Wise S, Stewart A. Nosocomial transmission of Mycobacterium tuberculosis from an extrapulmonary site. Infect Control Hosp Epidemiol 2001; 22:10-12.

In a cautionary tale that shows how insidiously tuberculosis can spread from an undiagnosed patient, the authors report TB infection in 12 health care workers.

Their findings suggest that there was minimal, if any, aerosolization of tubercle bacilli from
the patient’s lungs. Instead, transmission of TB occurred through aerosolization of tubercle bacilli from manipulation of the genitourinary wounds. The study underscores the extent of transmission among health care workers as a result of unrecognized genitourinary tract TB, the second most common site of extrapulmonary TB after lymphadenitis. As a result of the case, the authors recommend that infection control professionals consider airborne precautions for patients with open wounds of the genitourinary tract in whom bacterial cultures are negative, until a diagnosis of TB has been excluded.

The case occurred at a 275-bed community hospital in Middle Tennessee, where a patient was admitted for drainage of a prostatic abscess and a bilateral orchiectomy. He died after 27 days of hospitalization, and disseminated TB was then diagnosed at autopsy.

There was no evidence of active pulmonary tuberculosis throughout the patient’s hospitalization. TB skin test conversions occurred only among workers who were exposed to the patient during or after his surgical procedures. A total of 12 (13%) of 95 exposed health care workers who were previously nonreactive had newly positive tests. Those included six of 28 nurses, three of three autopsy personnel, two of 17 respiratory therapists, and one of 12 surgical staff.

The workers were all treated and cleared of infection. By logistic regression, irrigation or packing of the surgical site was the only independent risk factor associated with TB conversion among nurses. Manipulation of infected tissues of the genitourinary tract can result in nosocomial transmission of tuberculosis, the authors concluded.

Although the patient had microscopic evidence of pulmonary TB at autopsy, several factors argue against airborne transmission of TB from the respiratory tract. A chest radiograph on admission revealed no abnormalities, and there were no TB conversions among the 23 workers exposed to the patient prior to surgery.

Know the risk factors for persistent MRSA carriage

Low-level resistance to mupirocin also a factor

Harbarth S, Liassine N, Dharan S, et al. Risk factors for persistent carriage of methicillin-resistant Staphylococcus aureus. Clin Infect Dis 2001; 31:1,380-1,385.

Carriage of methicillin-resistant Staphylococcus aureus (MRSA) at multiple body sites and previous receipt of a fluoroquinolone are independent risk factors for persistent MRSA colonization in patients, the authors found. Low-level mupirocin resistance was observed in nine different MRSA strains, but was not independently associated with chronic MRSA carriage. However, even low-level mupirocin resistance may play a role in failure to eradicate carriage.

Mupirocin ointment was introduced in the United Kingdom in the mid-1980s and has subsequently been demonstrated to be highly effective in the eradication of nasal carriage of both methicillin-sensitive and MRSA strains.

However, reports of mupirocin-resistant strains of staphylococci have continued to appear since they were first described in 1987. Usage patterns that have promoted the emergence of mupirocin resistance include application of mupirocin ointment for long periods of time and its indiscriminate use within an institution.

The general consensus is that high-level resistant strains (MIC, >256 mg/mL) cannot be eradicated with mupirocin, whereas the clinical significance of low-level mupirocin resistance remains dubious.

The authors examined the risk factors for persistent MRSA carriage in 98 patients with MRSA colonization who were enrolled in a double-blind, placebo-controlled trial of nasal mupirocin. The probability of persistent MRSA colonization was almost two times greater among patients with more than one colonized body site and among patients who had recently received fluoroquinolones. Low-level mupirocin resistance tended to increase the risk of persistent MRSA carriage, whereas nasal mupirocin treatment tended to confer protection.

The findings may help explain the observed differences in the efficacy of topical eradication treatment in various groups of patients with MRSA carriage, the authors conclude.