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By Carol A. Kemper, MD, FACP, Clinical Associate Professor of Medicine, Stanford University, Division of Infectious Diseases; Santa Clara Valley Medical Center, Section Editor, Updates; is Associate Editor for Infectious Disease Alert.
MDR-TB in South African healthcare workers
Source: O'Donnel MR et al. High incidence of hospital admissions with multi-drug resistant and extensively drug-resistant tuberculosis among South African healthcare workers. Ann Intern Med. 2010;153: 516-522.
Admissions to a public tb hospital in KwaZulu-Natal, South Africa for treatment of MDR- and XDR-TB from 2003 to 2008 were examined for healthcare workers (HCWs) compared with non-HCWs.
During this period of time, 4,151 non-HCWs and 231 HCWs (≥ 20 yrs of age) with either MDR-TB or XDR-TB were admitted. From 2003-2008, the number of hospital admissions for MDR-TB increased from 440 cases to 1,028 cases (43 HCWs) and the number of admissions for XDR-TB increased from 6 cases to 114 cases (12 HCWs). The mean age and HIV status of the two groups were similar (55% of HCWs vs. 57% of non-HCWs were HIV+), although more of the HIV+ HCWs were receiving antiretroviral therapy.
The estimated incidence of MDR-TB in HCW admitted to hospital was 64.8/100,000 vs. 11.9/100,000 in non-HCWs; the incidence of XDR-TB in HCWs was 7.2/100,000 vs. 1.1/100,000 in non-HCWs. A key finding was that HCWs were significantly less likely to have received prior TB treatment than non-HCWs (41% vs. 92%, p < .0001), suggesting that while resistance may be acquired in non-HCWs as the result of inadequate treatment or non-compliance, HCWs were more like to acquire organisms already drug-resistant.
Nosocomial transmission of TB represents a significant threat to HCWs, and good airborne transmission precautions and appropriate facilities are essential. Not only are trained HCWs too valuable an asset for these countries to lose, but HCWs infected with TB present a safety risk to patients. A greater percentage of the HCWs with resistant TB in this study compared with non-HCWs were women (78% vs. 47%). Although the occupation of the HCWs were not specified, this finding suggests that women were more likely involved in direct patient care and, therefore, at greater risk for exposure.
Xpert MTB/RIF Assay for TB
Source: Boehme CC, et al. Rapid molecular detection of tuberculosis and rifampin resistance. N Engl J Med. 2010;363:1005-1015.
This article examines the specificity and sensitivity of the Xpert MTB/RIF test, which is an automated molecular test for detecting MTb and resistance to rifampin using real-time PCR in sputum specimen. A total of 1,462 patients were included in this project, 39% of whom had smear- and culture-positive pulmonary TB, 12% of whom had smear-negative and culture-positive pulmonary TB, and 7% of whom had a clinical diagnosis of pulmonary TB with negative smears and cultures. The remaining patients did not have TB and served as controls. Patients contributed 4,386 sputum samples for analysis. To briefly summarize the study's findings, the Xpert MTB/RIF test correctly identified 551/561 smear-positive specimens (98.2%) and 124/171 smear-negative specimens (72.5%). The sensitivity of the assay improved to 90.2% if three specimens were tested. The assay had a high degree of specificity, correctly identifying 604/609 negative specimens (99.2%). It correctly identified 97.6% of rifampin-resistant strains and 98.1% of rifampin-sensitive strains.
In a subgroup of 115 patients with culture-negative tuberculosis with suspected drug resistance, the Xpert MTB/RIF test identified 51 sputum TB specimens, eight with rifampin-resistance. All eight patients were subsequently treated with second-line therapy for suspected drug resistance although the clinicians were unaware of the results of the Xpert MTB/RIF research test results. Therefore, the assay successfully recognized drug resistance in patients receiving active treatment even after culture conversion.
Death and Resistance
Source: Levin PD, et al. End-of-life treatment and bacterial antibiotic resistance: A potential association. Chest. 2010;138:588-594.
Levin and colleagues examined the relationship between prolonged critical-care and end-of-life decisions and the presence of colonization or infection with drug-resistant bacteria. Culture results were reviewed for 423 patients receiving critical care in two different hospitals for more than 48 hours, and risk factors for acquisition of resistant bacteria were examined using logistic regression analysis.
Cultures yielded drug-resistant organisms in 82 patients (19%). Patients with drug-resistant organisms were more likely than those without to be diabetic and to have been transferred from another facility, and to have received a higher number of days of antibacterial therapy (19 vs. 14 days, p = .005). Although length of stay in the ICU was similar for both groups, patients with drug-resistant organisms required more prolonged mechanical ventilation (10 vs. 7 days, p = .03), had a greater number of central-line days (10 vs. 7 days, p = .03), and were significantly less likely to have had limitations of care ordered (11% vs. 26%, p = .014). The only independent risk factor identified in multivariate analysis was an order for limitation of care. At the time of death, 11% of those with limitations of care vs. 39% with ongoing critical care had recognized colonization or infection with drug resistant organisms (p = .003).
End-of-life critical-care treatment is associated with an increased risk of colonization or infection with resistant organisms. Not stated was whether critical-care patients were routinely screened for resistant organisms (e..g, nares, MRSA, screening cultures), as is being done in some hospitals. And it seems apparent that some bias may be introduced, as patients receiving ongoing critical care are more likely to have cultures performed. And rather than prolonged critical care increasing the risk of resistant bacteria but bacterial resistance may contribute to the need for more prolonged care and increased risk of death.
The authors suggest that, regardless of the causal relationship, patients receiving prolonged critical care present a "reservoir" for drug-resistant organisms in the hospital. The use of private rooms, contact isolation precautions, augmented surveillance, more aggressive environmental cleaning, and improved hand hygiene have all been demonstrated to mitigate this threat at significantly increased cost to hospitals.
MRSA Decolonization for Cardiac Surgery
Source: Walsh E, et al. Sustained reduction in methicillin-resistant Staphylococcal aureus wound infections after cardiothoracic surgery. Arch Intern Med. 2010; (pub. online Sept. 2010).
The state of California Health and Safety Code Regulations now require hospitals to screen certain high-risk groups within 24 hours of hospital admission for MRSA colonization, including patients admitted for total hip arthroplasty, total knee replacement, cardiac surgery, and any patient admitted from a long-term care facility (though expensive, this approach has helped to reduce hospital-onset MRSA rates). Unfortunately, these regulations do not provide guidance to physicians about what to do with a positive result, and often the result is available only after the procedure is completed.
Walsh and his group compared rates of post-operative wound infection 3 years before and 3 years following initiation of a MRSA intervention program. The program began by screening all 98 members of the cardiac surgery team (two nurses with nasal colonization received mupirocin). Subsequently, all cardiac surgery candidates were pre-screened for nasal colonization 24 to 72 hours before admission, or as soon as possible if transferred from an outside facility (swab cultures were performed on chromager plates using standard procedures); beginning the day prior to surgery, mupirocin intranasal ointment was used in all patients and continued for 5 days (regardless of MRSA screening culture results); chemoprophylaxis with parenteral vancomycin was given to all patients with recognized MRSA colonization (in addition to standard cefazolin prophylaxis); mupirocin-soaked dressings were applied to chest tube and mediastinal tube exit sites; and repeat nares screening cultures were done at discharge.
Prior to initiation of the program, rates of cardiac surgical site infection (SSI) were 2.1% (half of which was attributed to MRSA). Once the program was begun, a total of 2,496 patients were screened, and 56 (2.2%) had nasal colonization with MRSA. Three had persistently positive nares cultures at discharge. Following initiation of the program, the overall rate of cardiac SSI fell to 1.2, with a 93% reduction in MRSA SSI.
A difference in this study from other decolonization protocols was the use of mupirocin in all patients requiring cardiac surgery, not just those with MRSA. This eliminates the necessity of having culture results in hand when prescribing mupirocin the day prior to surgery although this approach increases mupirocin exposure and risk of resistance to this agent. Chemoprophylaxis with vancomycin was reserved for those patients with a positive culture result. The frequency of vancomycin adverse drug reactions and "red-man syndrome" are too great to risk the use of this agent in all patients, and would result in too many aborted procedures.
While the authors admit that hand hygiene rates also significantly improved during the period of observation, no mention was made of changes in pre-surgical scrubs. An alternative to the prophylactic use of antimicrobials, the use of improved chlorhexidine-alcohol pre-surgical scrubs also has been shown to significantly reduce the risk of SSI.1