Our study documented that 56.5% of the 184 health workers had a positive TST result reading; the prevalence rises to 64.3% when we include workers with previous positive TST results and a history of active TB disease. Both estimates are within the range expected for HCWs in low-income countries (33%) and middle-income countries (79%) [13]. Recent systematic reviews have found a prevalence of 49% and 37% with a mean incidence rate of active TB of 97 new cases per 100,000 HCWs [7, 8]. Our result is also slightly over the prevalence of 56% reported in a study among HCWs in Callao using IGRA [10]. These rates depict HCWs as a population at risk of developing active TB, since more than half of them are diagnosed with LTBI.
Similar to our study, Soto-Cabezas et al. in Peru, found a significant association between age and time working as a HCW with LTBI [10]. Likewise, Rafiza et al. in Malaysia found an increased prevalence of LTBI in employees with more than 11 years of work (OR: 3.48) and Pai et al. in India found an association with 10 or more years on the job, presenting a three-fold increase prevalence to those employed less than a year [16, 17]. An active TB patient with smear-positive sputum will infect on average between 10 to 15 people every year [18]; since most people will go to health care centers as their first point of contact regarding diagnosis, treatment, and monitoring of TB, it should come as no surprise that the longer time of employment on this health care setting could reflect repetitive exposure to M. tuberculosis. A study found a 10% probability of progression to active disease within a year for single exposure; furthermore, they established a greater probability of progression among individuals with 18 or more exposures [19].
We compared clinical and laboratory staff, whom we considered being a group of high-risk for transmission, against administrative workers and, although time spent with TB patients has been shown to be a risk factor [7, 13, 20, 21], our analysis did not find an association with LTBI. Additionally, health centers are bound to limited space with common waiting areas and most rooms are in near proximity to the area assigned for daily TB treatment, thus, TB exposure may be comparable between staff unlike in other settings such as large hospitals. Occupational differences in TST results prove difficult under these circumstances, in contrast to what has been found elsewhere [7]. Regardless of their occupation, the lack of association may be due to the staff’s exposure to the high prevalence of TB outside the health center or due to a household contact; moreover, TB infection may have occurred as children or TST positivity may be due to BCG universal vaccination at birth provided in Peru. Most of our participants were women, which is often the case in the healthcare setting as women constitute more than half of the healthcare workforce [12]. We found no association between gender and TST results.
The implementation of TB transmission control measures such as natural ventilation, a supply of N95 masks and routine screening, is essential to protect HCWs and may decrease annual TB incidence by as much as 49%, 27%, and 81% in countries with low, intermediate, and high TB incidence, respectively [22]. A risk assessment of obstacles in using N95 masks among HCWs ranked heat around the face and inaccessibility to masks as the main reasons for not wearing protective gear [23]. Our study found that 60.3% of HCWs did not wear N95 masks because the health center failed to provide them with the masks; this is a flaw in TB control which must be avoided in all settings, especially in a country with high TB incidence. Nonetheless, HCWs usually only wear masks when dealing with known TB cases, however, it is not common practice to continuously wear masks, therefore, transmission in healthcare facilities may be due to undiagnosed cases [24].
Only half of our participants had previous active TB screening during the last year; although these were standardized screening procedures by their place of work, we can see how the health center is unable to ensure TB screening for all its workers and some of them may have to access these tests out of pocket. Furthermore, considering the high LTBI prevalence found in our study, it seems unlikely that only 26 participants were exempt from TST application due to a previous positive TST result. It is likely that HCWs overreported having been tested in the last year, instead of underreporting a positive TST. In Portugal, from a sample size of 2015 registered physicians and nurses, a survey reported that 784 (39.5%) were never screened and, of these, 741 (94.5%) were never offered screening [25]. Moreover, in China, where no policy on medical TB surveillance among HCWs has been implemented, a large study identified 124 HCWs with presumptive active TB while noting that the screening methods and framework used is not yet optimal for the high-burden of TB in the country [26]. Establishing screening procedures for this high-risk population should be ensured either as routine or post-exposure to contribute to occupational health.
Even though 85.2% of participants agreed to take IPT if their result was positive, some refused the prophylaxis due to lack of knowledge including possible adverse events and immunological reactions or a belief of long-lasting immunity against TB. Although standards of TB care in Peru dictate that IPT must be administered to health workers and people attending prisoners, with a recent TST conversion after ruling out active TB [27], studies found acceptance rates for chemoprophylaxis amongst HCWs between 65-84% in low-prevalence settings [28, 29]. However, the use of IPT is debatable in settings of high rates of MDR-TB cases, as in Peru [1], which could explain why HCWs refuse the prophylaxis and prefer close monitoring of TB symptoms for at least two years, as per WHO recommendations [3]. Education and close monitoring of active TB symptoms must be provided for all HCWs, not only those who are TST positive.
Finally, some limitations must be recognized. Recall bias may have affected the participant’s responses to previous indentation or results for TST or whether or not they presented with a confirmed case of active TB. An important confounding factor is that we were not able to obtain a full picture of the participants before entering the health system for work: exposure to TB could have occurred before working as a HCW, especially if they lived in SJL or another high-burden area in Lima. This also includes reliable information on BCG vaccination. Self-reported use of N95 masks is not reliable as HCWs may feel compelled to overreport its use; additionally, the reported frequency of use is not quantitatively stated and, therefore, is open to interpretation by the HCWs completing the questionnaire. Other important variables were not significant in the multivariable analysis; this may be because the power of the study is less than needed to detect association due to the sample size.