Exposure to patients with active tuberculosis (TB) is considered an occupational risk for health-care professionals. The risk of TB transmission in health-care employees fundamentally depends on the type of care provided, the incidence of TB in the community and the implementation and compliance with TB prevention and control programs in health-care centers.1–3 These prevention programs should include periodical medical examinations of susceptible workers (with an initial risk evaluation and periodic follow-up), the use of adequate isolation measures and the diagnosis and early treatment of TB patients. There are studies that confirm that, in centers where control measures have been applied, the risk for contracting TB in health-care personnel is very similar to that of the community where they reside.4,5

In a recent review of studies on TB infection in health-care workers in countries with a low incidence of TB, the authors concluded that there is still a high risk for TB in the collectives that perform their occupational duties in certain risk areas.6 One of the causes for the increased risk of TB in health-care professionals in countries with a low incidence may be the delay in diagnosis.7,8 On the other hand, it may also be due to the higher number of immigrant health-care professionals coming from countries with a high prevalence of TB infection.

In Spain, there are few data available related with the magnitude of both infection as well as tuberculosis disease in health-care staff. The majority of the studies have been done in other countries where the epidemiological situation does not coincide with the Spanish situation.

The traditional screening test used in protocols of health-care personnel with occupational exposure to TB is the tuberculin test (TT).2 Recently, new tests are being introduced that are based on the detection of interferon gamma (IFN-γ) released as a response to the in vitro stimulation of the sensitized T cells in the peripheral blood with specific Mycobacterium tuberculosis antigens.9,10 In a previous study done in our center, we reached good agreement between the two IFN-γ tests (T-SPOT.TB and QFN-G-IT) for the diagnosis of TB infection in health-care personnel. In addition, both IFN-γ techniques were not affected by vaccination with BCG and they were more associated with occupational exposure than TT, possibly being more useful for detecting recent infection.11

The objective of this study was to estimate the prevalence of TB infection in the staff of a hospital over a 20-year period and to analyze the risk factors associated with this infection.

The baseline prevalence of TB infection throughout the study period was 25.7%, and it was higher in the first years (44.2%) than in the last years (15.8%). In comparison, the mean prevalence in health-care workers in high-income countries is 24% (range 4%–46%). In low-income countries, the mean prevalence is 63% (range 33%–79%).16

The levels found in the present study are very similar to those of the prevalence in the general population in Catalonia in the same periods.17 As the authors of this mentioned study comment, a series of factors should be kept in mind when comparing TB infection data published for the general population. Among others, the main factors are: the TT technique has varied throughout the years; many studies have been done with samples that are not representative of the general population or with very imprecise samples; and, not all studies have contemplated the BCG vaccination. The risk factors associated with positive TT have been sex (male), age, years of employment, vaccination with BCG and professional category. These factors have been found in other studies in which age18–20 and years of employment19–21 reflect a greater possibility of having been in contact with tuberculous patients. The baseline prevalence was higher in non-health-care personnel and orderlies (38.9% and 46.8%, respectively). This may be due to the fact that the mean age of these collectives was higher than that of the health-care staff (mean age among non-health-care personnel was 34 vs 32 among the health-care staff, with a P<.001), although when adjusted for age the prevalence has continued to be higher in these collectives. One explanation could be, on the one hand, that they may have less epidemiological knowledge about the disease and, on the other, that they may have other non-occupational risk factors (place of residence, socioeconomic level) that have not been dealt with in this paper. In a study done in the city of New York,18 a higher baseline prevalence was also found in non-health-care personnel (maintenance, cleaning and security personnel). The authors argued that these workers had brief contact with the patients, but on a daily basis, and that they gave little importance to the use of protection measures, such as masks. In addition, as these professionals historically have not been considered groups at risk for TB, they are not included in training programs about preventive measures.

The percentage of “booster effect” found in our hospital (10.8%) is higher than that reported in other studies,22,23 with percentages of 5.2% and 2.8%, respectively, despite the fact that the epidemiological situation and vaccination with BCG is different in our setting.

The baseline prevalence was higher in the early periods than in the last years of the study. This could be due to various factors: in the initial years, both TB incident cases as well as prevalent cases were detected. Furthermore, there was a reduction in the incidence of patients with TB admitted to the hospital (from 150 annually at the beginning of the study to approximately 50 in recent periods). It may also be related with an improved compliance of the nosocomial TB control measures that have been implemented in the hospital over the course of the study period.24–26

It has been reported that when there are fewer patients admitted with TB, there is a delay in diagnosis.27 Along this line, in recent years ten contact studies have been done in our hospital in health-care workers who had experienced accidental occupational exposure to bacilliferous patients without measures of protection. Out of the 133 professionals studied, 5 cases of tuberculin conversion were detected and no cases of TB related to the exposure were found (unpublished data). Practically all these accidental exposures have been due to delay in the diagnosis of TB in patients. From the information available, we have seen that the maximum time without diagnosis was 2 weeks, with a mean of 8.4 days.

The higher prevalence data in the early periods could also be partially explained by the vaccination with BCG (the percentage of BCG vaccine recipients was higher in the early years). In Catalonia, between 1965 and 1980, millions of people were vaccinated. Although the vaccination history is registered systematically and the presence of the corresponding scar is verified, some individuals may have been included with positive TT due to the vaccine, and consequently the TB infection may have been overestimated.

One must also keep in mind the influence of immigration in recent years on the prevalence of infection and on the incidence of TB in the general population and that it may also have had an influence on health-care staff. This has happened in the United States,28 where it was found that the factors that are independently associated with the conversion of TT in health-care personnel were having been born outside of the United States and having a TT in an occupational contact study. In our setting and in our hospital, the number of immigrant staff members is still low but has been growing in recent years.

Lastly, it must also be taken into account that the community risk was not analyzed, and therefore we cannot rule out TB infection community transmission. The data were not adjusted for either area of residence of the workers or for socioeconomic level. According to Sepkowitz,29 in hospitals where few annual TB cases are admitted is where the community transmission could be more important than occupational transmission in hospital workers.

In summary, the data provide information about the evolution of TB infection among the employees at a third-level hospital over the course of a 20-year period. The prevalence of TB among the hospital staff is high, although it did decline over the period studied, which also coincided with a lower TB incidence in the reference community and fewer patients admitted with TB. In spite of this, due to the fact that when the number of patients admitted drops, the delay in diagnosis increases, it is important to continue with TB vigilance and control programs for hospital employees in order to determine the tuberculin state. At the same time, these programs should include training for health-care personnel, especially centered on the identification of the signs and symptoms of TB, its transmission mechanisms and the nosocomial prevention measures for the disease.

The authors declare having no conflict of interests.