Latent Tuberculosis in Healthcare Professionals: A Cross-Sectional Study

Abstract

Tuberculosis (TB) is a dangerous disease caused by the bacterium Mycobacterium tuberculosis. Its transmission occurs through aerosols, making healthcare workers particularly vulnerable to it. At the San Cecilio Clinical University Hospital in Granada (HUCSC), preventive measures such as the use of personal protective equipment (PPE) and IGRA (interferon-gamma release assay) tests were implemented to detect latent tuberculosis infection. At HUCSC, between 2022 and 2024, 4.75% (92/1936) of workers were found to have positive IGRA test results, with no significant differences observed between professional categories. However, variability in positive IGRA rates was noted across different medical departments, with pulmonology and sample handling being the most affected. Additionally, a relationship was found between age and the likelihood of obtaining a positive IGRA test result. These findings underscore the importance of targeted preventive measures and a multifaceted approach to controlling and preventing tuberculosis in workplace environments.

1. Introduction

Tuberculosis (TB), caused by the bacterium Mycobacterium tuberculosis, poses a significant danger to the human population, with high prevalence among groups with a low socioeconomic status [1].

Its primary reservoir is infected humans, and sick individuals are the source of infection, especially those presenting with a cough, pulmonary cavitary lesions, and acid-fast bacilli (AFB) in their sputum. Its main route of transmission is airborne, through contaminated aerosols from air exhaled by infected individuals. These droplets, measuring 1 to 5 microns in diameter, can remain suspended in the air for hours [2,3].

In the hospital setting, exposure to Mycobacterium tuberculosis is a well-documented risk. Healthcare workers may come into contact with patients with active TB, contaminated biological samples, and aerosol-generating procedures, increasing the risk of transmission. According to the guidelines by Casas et al. [4], healthcare workers are estimated to have three times the annual risk of developing TB compared to the general population. This risk varies across work areas and units, with higher exposure in emergency departments, microbiology laboratories, and pathology units [2,5].

Exposure to biological agents in the workplace is a critical concern in occupational health. According to Royal Decree 664/1997 on the protection of workers from risks related to their exposure to biological agents at work, employers are required to assess these risks and take appropriate measures to protect workers. This regulation mandates the implementation of health surveillance programs that include diagnostic tests and appropriate preventive measures [6].

It is therefore essential to have an effective surveillance program that includes periodic testing to detect latent tuberculosis infection. At the San Cecilio Clinical University Hospital in Granada (HUCSC), preventive measures have been implemented to minimize the risk of TB transmission among healthcare workers. These include the use of personal protective equipment (PPE), such as N95 or FFP2 masks for staff in direct contact with TB patients, control of ventilation systems, negative pressure rooms for patients with active TB, and periodic health surveillance, including the use of interferon-gamma release assays (IGRAs) to monitor staff exposure [7].

An IGRA test is a useful diagnostic tool for detecting latent TB infection, and it is the preferred method at HUCSC due to its advantages over the Mantoux or tuberculin skin test, including its higher specificity (as it is not affected by BCG vaccination), reducing the number of false positives. Additionally, an IGRA only requires a single blood draw, and its results are obtained quickly [8].

This study will analyze the IGRA test results of healthcare workers at HUCSC during 2022, 2023, and 2024.

In Spain, a Tuberculosis Prevention and Control Plan for the years 2019–2030 is currently in place, outlining that the incidence rate of tuberculosis has decreased from 9.39 cases per 100,000 inhabitants in 2019 to 7.83 per 100,000 in 2022, exceeding the target set for 2020 [9].

Despite this, the primary objective of this study is to identify positive cases and assess their distribution across different departments and professional categories. Additionally, the potential correlation between workers’ age and the likelihood of a positive IGRA test result will be investigated. This is crucial for a better understanding of the TB transmission dynamics in hospital environments and for developing more effective prevention and control strategies. Through analysis of the collected data, this study aims to provide valuable information that will contribute to improving the health and safety of healthcare professionals at HUCSC. Identifying the departments and professional categories with the greatest contact with TB will allow for a more targeted focus on preventive and control measures, thus enhancing the effectiveness of occupational health programs within the hospital. Specifically, the following research questions were proposed:

• Are there certain professional categories that exhibit a higher risk of testing positive in the IGRA test?
• To what extent do certain departments have a higher incidence of contact with tuberculosis-infected patients?
• Is there an association between older age and a greater likelihood of obtaining a positive result in an IGRA test?

2. Materials and Methods

2.1. Study Design

A cross-sectional descriptive study was conducted by the Occupational Health Department at San Cecilio Clinical University Hospital in Granada (HUCSC). The report of this research adheres to the STROBE guidelines for descriptive studies [10].

2.2. Setting

Participants were recruited through non-probability convenience sampling when they attended health examinations from 1 January 2022 to 1 June 2024, including both new employees and routine check-ups for existing workers.

In accordance with the established protocol, participants who already had a recent IGRA test result recorded in their medical history were excluded. This measure ensured the integrity of the data and prevented duplication in the information collected.

Additionally, according to the same protocol, all workers who presented a positive IGRA test result underwent a chest X-ray and were referred to internal medicine for further evaluation.

2.3. Participants

The following inclusion criteria were applied:

• Workers exposed to biological risks.
• Professionals who attended a health examination during the study period.
• Workers for whom an IGRA test was requested.

The following exclusion criteria were applied:

• Workers on temporary disability leave.
• Workers employed by external contracting companies.
• Workers with a previous positive IGRA or Mantoux test.

2.4. Variables and Data Sources

Data coding was pre-planned prior to the data collection, with the data extracted directly from medical records into a structured database, such as WinMedtra. The variables under study were obtained from the “Analytics” section of the health examination.

The variables collected in this study encompassed several aspects relevant to the analysis. First, the age of the participants was considered, and they were grouped into the following categories: 20–29 years, 30–39 years, 40–49 years, 50–59 years, and 60 years or older. This range allowed for the observation of differences in the results across various life stages.

Another important variable was gender, distinguishing between men and women to identify any potential gender-based differences in the results obtained. The nationality of the workers in the sample was analyzed, classifying them into two groups: those with Spanish nationality and those without Spanish nationality.

The professional category of the subjects was also a key variable, covering various healthcare professions, such as nurses, doctors, nursing assistants, orderlies, specialist technicians, kitchen staff, and a diverse group including psychologists, speech therapists, social workers, and physiotherapists. This categorization allowed for an analysis of the impact and differences between the various roles within the hospital setting. To ensure an adequate level of precision in comparing the IGRA test positivity prevalence across the professional categories, a power analysis was conducted. Using a 95% confidence level and 80% statistical power, it was estimated that a minimum of 70 workers per category would be required to detect significant differences with an acceptable margin of error based on an overall positivity rate of 4.75% in the general population. This approach ensures that the categories included in the analysis had a sufficient sample size to maintain the robustness of the results and to minimize the risk of Type II errors (false negatives).

The results of the IGRA tests were evaluated, classifying the participants based on whether their test results were positive or negative, which is crucial for the study of latent tuberculosis infections.

In addition, the medical department in which the participants worked was considered, grouping them into specific areas for a more detailed analysis: surgical and trauma areas; anesthesia; medical specialties (including neurology, cardiology, gastroenterology, endocrinology, and mental health, among others); diagnostic and treatment support (including pharmacy, nuclear medicine, radiology, radiopharmacy, and radiophysics); sample handling (laboratory, microbiology, and pathology); catering; maternal and child areas (gynecology and pediatrics); and rotating staff without a service assignment. This classification enabled an examination of how different work environments could influence this study’s outcomes.

Finally, due to their particular relevance in treating respiratory-transmitted diseases, the pulmonology, ICU, and emergency departments were included separately, allowing for a specific analysis of these high-risk environments.

2.5. Study Size

HUCSC is the second referral hospital in the province, with a total workforce of 4132 employees at the time of the study.

To determine the sample size required for our study, we started with a total population of 4132 hospital employees. The sample size was calculated using a finite population approach, considering a 95% confidence level and a 5% margin of error. Since the exact proportion of the population exhibiting the characteristic of interest was unknown, we adopted a conservative estimate of 50%, which maximized the necessary sample size.

During the data collection, a 3.2% attrition rate was observed, corresponding to the loss of 66 cases. To ensure that the final sample remained representative of the total population, we adjusted the initial sample size to account for this attrition.

After applying the adjustment for the attrition rate observed, the initial sample size was increased, resulting in a final sample of 1936 employees included in the analysis. We considered this final sample to be appropriate and representative of the total population of 4132 hospital workers.

2.6. Statistical Methods

In this study, a descriptive analysis of the qualitative variables was performed using absolute frequencies and percentages, while the quantitative variables were analyzed using means and standard deviations or medians and ranges. To compare the proportions of positive IGRA tests among different professional categories, the Chi-square test for homogeneity was employed.

Confounding variables were controlled through multivariable statistical analysis. These measures ensured the validity and reliability of the findings obtained in this descriptive study.

2.7. Ethical Statement

An informed consent document was developed and signed by the professionals who participated in the health surveillance, in accordance with Law 3/2001 of 28 May, which regulates informed consent and the medical history of participants. They were informed of their voluntary participation and their right to withdraw from the study at any time, with the understanding that their anonymized results could still be used, as per Royal Decree Law 6/2012. Additionally, the Organic Law 3/2018 of 5 December, on Personal Data Protection and Digital Rights, was explained to them.

3. Results

3.1. Are There Certain Professional Categories That Exhibit a Higher Risk of Testing Positive in the IGRA Test?

The overall proportion of positive IGRA tests was 4.75% (92/1936). By professional category, the distribution was most prevalent among kitchen assistants and nursing auxiliaries (see

Table 1. Prevalence of positive IGRA tests by professional category.

Professional Category	Positive IGRA Test	Negative IGRA Test
Orderlies	10	218
Nurses	26	605
Doctors	14	427
Nursing Assistants	29	406
Specialist Technical Staff	9	137

). With a Chi-square = 8.367, the p-value = 0.212. In response to the research question “Are there certain professional categories that exhibit a higher risk of testing positive in the IGRA test?”, the data indicate that there are no significant differences in the prevalence of IGRA positivity across professional categories relative to the overall proportion. Of the total sample, 3.36% were foreign workers, of whom 5.2% tested positive in the IGRA (p > 0.05).

A further analysis was conducted for categories with a sufficient sample size (≥70 workers). All the categories were representative except for kitchen assistants (within the hospitality category) and “other categories” (fewer than 70 professionals). With a Chi-square = 7.32, the p-value = 0.121, so we can confirm that there were no significant differences in IGRA positivity among the professional categories.

Of the 92 positive cases, there were 4 that tested positive but for whom the professional categories to which they belonged did not consist of 70 or more individuals.

3.2. To What Extent Do Certain Departments Have a Higher Incidence of Contact with Tuberculosis-Infected Patients?

To determine the necessary sample size for each of the 15 medical services to ensure representativeness and enable comparisons among them, we followed a similar approach to that used for the professional categories. The calculation was based on the overall proportion of positive IGRA tests in the population (4.75%) and the ability to detect a significant difference with a 95% confidence level and 80% power. Despite the hospitality and pulmonology staff not constituting a representative sample, the analysis proceeded.

A Chi-square test for homogeneity was conducted to evaluate the differences in the proportions of positive IGRA results among different medical services. The data were grouped into 12 representative services (see

Table 2. Distribution of IGRA test results by medical service.

Medical Service	IGRA Test Results
	Positive	Negative
Anesthesia	7	114
Diagnostic Support	5	110
Maternal and Child Areas	9	228
Surgical Area	13	184
Medical Specialties	17	410
Internal Medicine	8	96
Sample Handling	7	80
Pulmonology	8	37
Rotating Staff	3	226
ICU	5	109
Emergency	8	229
Hospitality	2	21

). The Chi-square test revealed significant differences in the proportions of positive IGRA results among the different services (Chi-square = 31.62, p-value > 0.001). These results indicate significant variability in the IGRA positivity rates depending on medical service.

To identify the specific differences in the IGRA positivity rates among the medical services, a post hoc analysis was conducted using multiple comparisons with the Z proportion test and Bonferroni adjustment. Multiple comparisons among the IGRA positivity rates across services revealed several statistically significant differences. In particular, the pulmonology service showed significantly higher rates of positive IGRA results compared to all the other services. Other services with significantly high rates include sample handling and internal medicine.

3.3. Is There an Association between Older Age and a Greater Likelihood of Obtaining a Positive Result in the IGRA Test?

Regarding the distribution of positive IGRA test results by age group, the results obtained were as follows (see

Table 3. Prevalence of positive IGRA tests by age.

Age Group	Prevalence of Positive IGRA Tests	Proportion of Workers with a Positive IGRA Test
20–29 years	0.89%	3/338
30–39 years	3.15%	14/444
40–49 years	5.36%	27/504
≥50 years	7.38%	48/650

). In the age range of 20–29 years, there were only 3 positive cases; in the 30–39 years range, there were 14 positive cases; in the 40–49 years range, there were 31 positive cases; and in the 50 years or older range, there were 48 positive cases. The Chi-square test indicated that the differences in the IGRA positivity rates among the different age groups were statistically significant, with a Chi-square = 47.542 and a p-value < 0.001.

4. Discussion

This study, conducted at the Hospital Universitario Clínico San Cecilio de Granada (HUCSC), focused on the prevalence of latent tuberculosis infections (positive IGRAs) across different professional categories and medical services. The overall prevalence of positive IGRA results was 4.75%, which is notably lower than the figures reported in previous studies, which have estimated the LTBI prevalence among healthcare workers to be between 11.1% and 13.3% in high-income countries and around 28% in low- and middle-income countries [5,11]. This difference may be partially explained by the overall decrease in the incidence of tuberculosis in Spain in recent years, as reflected in the Epidemiological Report on the Tuberculosis Situation in Spain [12].

Contrary to our initial research question, no statistically significant differences were found in the IGRA positivity rates among different professional categories. This finding differs from previous studies that have identified certain categories, such as resident physicians or nursing staff, as higher-risk groups [13,14]. However, it is consistent with the results of Pérez Bermúdez et al. [15], who also found similar prevalence rates across different professional categories.

The analysis by medical service revealed significant differences in the IGRA positivity rates, with services such as pulmonology and sample handling exhibiting the highest rates. These results align with the existing literature, which has identified high-risk areas such as pulmonology services, emergency departments, and microbiology laboratories [5,16,17].

The significant relationship found between age and the likelihood of obtaining a positive IGRA test result is consistent with previous studies [15,18]. This finding may be explained by greater cumulative exposure over the course of a working life, as well as the possibility of past exposure in the context of a higher tuberculosis incidence in previous decades.

This study has several limitations that should be considered when interpreting its results. One major limitation is the lack of representativeness in certain professional categories and medical services, particularly in the pulmonology and hospitality services, which did not achieve a sufficient sample size. This lack of representativeness could introduce bias into the estimation of the prevalence of IGRA positivity in these groups.

Additionally, the non-probabilistic convenience sampling methodology may have introduced selection bias, limiting the generalizability of the results to the entire hospital workforce. Data loss due to laboratory errors may also have affected the accuracy of the results, although this was minimized through appropriate statistical control of confounding variables.

This study’s results suggest that while the overall prevalence of positive IGRA tests among HUCSC workers is relatively low, there are significant differences among the different medical services. This indicates that the risk of exposure to latent tuberculosis is not uniform across the hospital, which may be related to the different activities and levels of exposure associated with each service.

The lack of significant differences among professional categories, contrary to what has been observed in some previous studies [13,14], might suggest that the preventive measures implemented at HUCSC have been effective in reducing the risk disparities among different worker groups. However, the high prevalence in specific services such as pulmonology and sample handling is consistent with existing literature [16,17,19] and highlights the need for reinforced preventive measures in these areas.

The observed relationship between age and IGRA positivity is consistent with previous studies [15,18] and may reflect both cumulative exposure over a working lifetime and possible past exposure in the context of a higher tuberculosis incidence in the past. This finding underscores the importance of considering age as a risk factor in occupational health surveillance programs.

The generalizability of this study’s results is limited by the specific characteristics of the sample and study design. Although HUCSC is a referral hospital, its working conditions, its preventive practices, and the demographic characteristics of its workforce may differ significantly from those in other hospitals, both nationally and internationally.

Nevertheless, the general patterns observed, such as the variability in the IGRA positivity rates between services and the relationship between age and IGRA positivity, are consistent with existing literature [18,20] and may be relevant to other hospital settings. The methodology used and the lessons learned regarding the importance of considering service-specific factors in assessing the risk of latent tuberculosis could be useful for informing similar studies in other contexts. Implementing periodic screening programs with IGRAs, especially in high-risk services, could be an effective strategy for the early detection and management of LTBI among healthcare workers [21].

5. Conclusions

In conclusion, this study provides detailed insight into the prevalence of latent tuberculosis infection (LTBI) in a specific hospital setting, highlighting the importance of preventive approaches tailored to the occupational risks present in different medical services. Despite its limitations, these findings underscore the need for ongoing research to confirm these results and assess their applicability in other contexts. The implementation of targeted preventive strategies and continuous monitoring is crucial for protecting the health of healthcare workers and preventing the transmission of tuberculosis within a hospital environment.