Bmc Infectious Diseases Increased Risk of Tuberculosis in Health Care Workers: a Retrospective Survey at a Teaching Hospital in Istanbul, Turkey

Background: Tuberculosis (TB) is an established occupational disease affecting health care workers (HCWs). Determining the risk of TB among HCWs is important to enable authorites to take preventative measures in health care facilities and protect HCWs. This study was designed to assess the incidence of TB in a teaching hospital in Istanbul, Turkey. This study is retrospective study of health records of HCWs in our hospital from 1991 to 2000.


Background
Tuberculosis (TB) is an established occupational disease of health care workers (HCWs) and those infected may transmit the disease to susceptible individuals. Previously, it has been reported that HCWs are at increased risk of TB [1][2][3][4][5][6]. There is a large number of studies from North America about the risk of TB among HCWs and TB control programs have been established to protect HCWs in these countries. Prevalence of TB among HCWs in high-prevalence countries has been poorly documented [4][5][6] and TB control programs are not widespread. Turkey is one such country and had a TB incidence of 26.3 per 100,000 in 2000 [7]. Also, in Turkey there is no central control program for the prevention of TB in HCWs. Determining the risk of TB among HCWs is important to enable authorites to take preventative measures in health care facilities and protect HCWs. TB than the normal population and if the incidence of TB varies between hospital departments.

Methods
This retrospective study was performed at the bed acute care hospital of the Istanbul Medical Faculty. We reviewed health records of HCWs from 1991 to 2000, obtained from the Department of Chest Diseases and Human Resource Department archives. TB is diagnosed by bacteriological culture or histological evidence of granuloma with caseafication necrosis or clinical findings consistent with active TB (fever, sputum, malaise, fatigue, loss of apetite, weight loss, night sweats) and full course of chemotherapy is indicated for these patients.
Demographic data for HCWs were provided by the Human Resources Department of the hospital. Population in December was taken as the study population for each year. Incidence rates of TB for Turkey's general population were taken from the annual statistics report of the Ministry of Health [7].
The Department of Chest Disease was evaluated separately from the Department of Medicine. The Department of Basic Science was including laboratories as Microbiology, Pathology, Pharmacology, Biochemistry, Forensic Medicine and Physiology. Managerial department and services were including the Dean's Office, Human Resource Office, laundry, central kitchen, mechanics, central heating unit, accommodation and student affairs

Results
Between 1991 and 2000 the mean work force of the hospital was 3359 ± 33.2, consisting of 879 doctors, 670 nurses and 1810 allied health professionals. There were 31 cases (15 male, 16 female) meeting the diagnostic criteria for TB. Thirteen cases were confirmed by sputum culture and one by urine culture, eight cases were verified by histological examination, and nine patients showed findings consistent with active pulmonary TB. The 31 cases of TB comprised eight doctors, one nurse and 22 other health professionals. Mean age was 35 (range: 22-50) for doctors, 27 for nurse and 25.7 (range 19-58) for other professionals. All of the TB patients had worked as an HCW for at least 12 months.
Twenty three of the cases were pulmonary TB and 8 were extra-pulmonary. In the pulmonary TB patients, chest xray revealed typical lung parenchyma pathology. There were no cases of active TB in the families of HCWs.
Mean incidence of TB for 1991 to 2000 was 96 per 100,000 for all HCWs (relative risk: 2.71), 79 per 100,000 for doctors (relative risk: 2.2), 14 per 100,000 for nurses and 121 per 100,000 (relative risk: 3.4) for other profes-sionals. Mean incidence of TB for Turkey as a whole was 35.4 per 100,000 [7]. Fig. 1 shows the incidence of TB in our study and in the general population.
Incidence rates were similar in the Departments of Chest Diseases (151 per 100,000) and Medicine (157 per 100,000). Incidence in the Department of Surgery was lower, at 107 per 100,000. There were no cases of TB in the Basic Science and Managerial Departments.

Discussion
In our study the results indicated that the incidence of TB among hospital staff was approximately three times more than that in the general population of Turkey. Previous studies made by Turkish hospitals also showed that risk of TB among HCWs was higher than in the general population [8].
The demographic characteristics of TB cases among our hospital HCWs were different from the general population. In Turkey, it has been shown that TB is more common among persons with a mean age of 37.5 years (range 20-39) and 85% of patients are male [9]. However, in our hospital staff, the mean age of TB patients was 27.7 years and 50 % of them were female. These differences support the idea that TB in HCWs was of nosocomial origin.
There are two limitations in our study. First, we do not have information about staff that left the hospital to pursue another occupation. Our data was limited to the time that they worked in the hospital. The second limitation concerns the incidence rates of TB in the general population. We accepted the Ministry of Health figures but we estimate that the reported incidence rates are less than the

Figure 1
The comparison of the incidence of tuberculosis for health care workers (HCWs) and the general population by years. Between 1991-2000, mean incidence of Tuberculosis for HCWs is three times more than general population  [4]. Similar results have been found in Serbia [5], Malawi [6], Japan [10], North America and Western Europe [12][13][14]. However, two studies had different findings [15,16]. Firstly, in the UK, McKenna showed that risk of TB among HCWs was similar to that of the general population. Secondly, Raitio found that the overall risk of TB among HCWs was lower than in the general population. The incidence of TB in Turkey in 2000 of 26.3 per 100,000 is lower than the rates in Estonia, Malawi and Serbia but higher than North America and Western Europe. Nevertheless, our results are in line with those of other countries.
In Turkey there is no specific TB prevention program for HCWs. There are several chest clinics where HCWs and TB patients use surgical masks but there is only one clinic which has negative ventilation for its TB ward. In North America, on the other hand, TB prevention programs for HCWs have been established and performance is regularly controlled [17]. In spite of this structural difference, the similar, higher TB risk for HCWs in Turkey and North America is significant. In our Department of Chest Diseases, the last TB case in an HCW was in 1991. Surgical masks have been used in the department since 1992. A separate TB ward was set up in 1996 and in 1998 it was fitted with a central negative ventilation system. We observed that in other hospital departments, with the exception of nurses, staff did not take precautions against TB. The incidence of TB among nurses was very low in comparison with other staff. All the nurses in our hospital have a regular postgraduate education program but the doctors and other staff do not. We speculate that the low incidence of TB in nurses is dependent on this regular education. TB is still a disease that affects low income groups in Turkey. The level of income for HCWs is higher than the poverty threshold. Indeed, the incidence of TB in that income group would have been expected to be lower than in the general population.
Unfortunately, we do not have detailed information about TB in Turkey that takes account of different income levels. However, we predict that TB incidence in nurses in our hospital will be similar to non-medical personnel who have the same income as HCWs. Two other factors may account for the different TB risk in nurses compared with other health professionals. Nurses usually work in wards where it is known if a patient has TB, therefore, nurses can take steps to protect themselves against infection. Doctors and other health professionals work in outpatient and several other departments at the same time. In these circumstances there may be patients with undiagnosed TB, leading to increased risk of infection.
Although the risk of TB was higher in all clinical specialties than in the general population, the incidence of TB in surgery and pediatrics was lower than in other clinical departments. This could be because TB patients are not usually admitted for surgery and transmission of TB from children is unusual. There have been no TB cases in the Basic Science Department for last ten years, even though this department has both pathology and microbiology laboratories. However, adult autopsies have been performed rarely in the pathology laboratory since 1991. The microbiology laboratory performs a limited number of sputum examinations for Mycobacterium tuberculosis, given that there is another specialized laboratory in Istanbul for this purpose.

Conclusions
HCWs in Turkey, especially those working in clinics, have an increased risk for TB. Post-graduate education and preventative measures reduce the risk of TB. Control programs to prevent nosocomial transmission of TB should be established in hospitals to reduce the risk for HCWs.

List of abbreviations
HCWs: Health care workers TB: Tuberculosis