Original Research: Tuberculosis infection in healthcare workers
Risk factors for latent tuberculosis infection among healthcare workers in a university-affiliated hospital M Nassaji, R Ghorbani
Mohammad Nassaji, Department of Infectious Disease, Fatemieh Hospital, Semnan University of Medical Sciences, Semnan, Iran Raheb Ghorbani, Department of Social Medicine, Semnan University of Medical Sciences, Semnan, Iran E-mail:
[email protected];
[email protected]
Healthcare workers represent an important risk group for exposure, infection, and potentially disease by Mycobacterium tuberculosis. The aim of this study was to assess the prevalence and risk factors for latent tuberculosis infection among healthcare workers in a teaching hospital. A cross-sectional study was conducted in 2009 at the Fatemieh Hospital, Semnan, Iran. Information about age, gender, occupation, history of BCG vaccination and duration of employment was obtained by a structured questionnaire. All subjects received a Mantoux tuberculin skin test. Induration of ≥10 mm was considered a positive test. A total of 180 healthcare workers (60.5% female, 39.5% male) were enrolled. Twenty-five (13.9%) had a positive skin test. History of BCG vaccination was detected in 159 (88.3%) of participants. In logistic regression analysis, employment for >five years (OR=4.10; 95% CI, 1.07-15.68) and for >10 years (OR=4.59; 95% CI, 1.45-14.59) was significantly associated with increased risk of a positive test. Age, gender, history of BCG vaccination and type of occupation were not significantly associated with a positive TST response. A low prevalence of latent tuberculosis infection was found among healthcare workers in this hospital. Longer duration of employment was significantly associated with increased risk of positive tuberculin skin test. South Afr J Epidemiol Infect 2012;27(1):30-33
Peer reviewed. (Submitted: 2011-03-08. Accepted: 2011-08-18.) © SAJEI
Introduction
decline in the incidence of TB and more recently through the institution of effective infection control measures to reduce transmission of TB in healthcare facilities.7
Mycobacterium tuberculosis infects one-third of the world’s population and is known as latent tuberculosis infection (LTBI). Some infected individuals (10-15%) are at risk of developing disease especially within the first year or two after infection.1
The World Health Organization (WHO) published guidelines on the prevention of TB in healthcare facilities in resourcelimited areas in 1998 and an addendum to those guidelines was added in 2006. The recommendations place emphasis on administrative controls, including careful screening and prompt diagnosis of TB, separation of TB patients from other patients and rapid treatment of TB.8
Healthcare workers (HCWs) represent an important risk group for exposure, infection, and potentially disease by M. tuberculosis. However, the risk varies widely among the various occupational groups and according to their working conditions.2
The tuberculin skin test (TST) has been available for more than 100 years for the diagnosis of LTBI. The TST measures a delayed type hypersensitivity response to purified protein derivative (PPD), a mixture of antigens shared among mycobacteria.9 TST still plays an important role, because it is the only widely used method of detecting M. tuberculosis infection. The size of the TST reaction is used to classify individuals according to their likelihood of infection. But, the TST has its limitations, including cross-reactivity to BCG vaccination strain and several non-tubercular mycobacteria.10 The Centers for Disease Control and Prevention recommend performing a two-step TST on all newly employed HCWs to identify HCWs who have had infection. On May 2005, interferon gamma release assay testing received final approval from the
This occupational hazard received little attention until numerous outbreaks of tuberculosis (TB) occurred in hospitals. The prevalence of LTBI in the healthcare setting ranges from 11% to 30% in higher-income countries.3 In low-income countries it is estimated that prevalence is between 60% and 80%.4 In low-income countries the risk of TB among HCWs has received less attention. Many studies showed higher burden of infection in this groups when compared with the general population.5 Therefore, the screening of HCWs for LTBI is crucial in an infection control programme.6 The risk of infection in HCWs has been reduced in many countries as a result of an overall
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2012;27(1)
Original Research: Tuberculosis infection in healthcare workers
Food and Drug Administration for diagnosing M. tuberculosis infection that has greater specificity than TST. 11
The duration of employment was less than five years for 41.6% of HCWs, five to 10 years for 17.8% of HCWs and >10 years for 40.5% of HCWs. The mean (±SD) duration of employment in the hospital was 10.2±7.6 years. Of all of the participants, 43.2% were nurses (including staff nurses and assistant nurses), 30.5% were administrative staff, 21.6% were laboratory workers and 21.6% were housekeeping staff. The history of BCG vaccination and presence of scarring due to the application of the BCG vaccination were noted in 159 of the individuals (88.3%).
Iran is one of the countries that has made progress in the TB control programme in recent years. Medical care for TB in Iran is provided through the national TB programme and directly observed treatment short course (DOTS) strategy coverage is good. The incidence of TB cases in Iran decreased from 34.46/100,000 in 1992 to
