Tuberculosis: Occupational risk among dental healthcare workers and risk for infection among dental patients. A meta-narrative review

Abstract

Objectives

Tuberculosis transmission among healthcare workers (HCWs) and patients is due to the level of Mycobacterium tuberculosis (MT) circulation in the community and in the healthcare settings where HCWs are active. In contrast, most papers about dentistry report that dental HCWs (DHCWs) and patients are at relatively high risk, mainly based on tuberculosis case series that occurred in the 80’s–90’s. This meta -narrative review was designed to evaluate the tuberculosis risk in dentistry accounting for the historical-geographical contexts.

Data

All available studies reporting data on MT infection (active/latent tuberculosis, tuberculin skin test) among patients and DHCWs.

Sources

PubMed, Scopus, GOOGLE Scholar.

Keywords

MT/tuberculosis and dentistry/dentist/dental/dent*.

Results

238 of the 351 titles were excluded because did not concern dental healthcare providing, 94 papers were excluded because they did not provide original data. Thirteen studies on occupational risk, nine on transmission to patients remained. Some, often non-confirmed, cases of MT infection among patients were reported in specific historical-geographical contexts where MT was endemic. The risk of active pulmonary tuberculosis transmission from infected DHCWs to patients is minimal today, provided that the basic infection control guidelines are applied. The development of active tuberculosis among DHCWs is occasional and is associable to MT circulation rather than dental healthcare providing.

Clinical significance

Tuberculosis transmission in dental healthcare settings was due to the lack of basic infection control measures, while the risk is acceptable (i.e., similar to the general population) nowadays. Therefore, tuberculosis transmission can be safely prevented wearing gloves and surgical mask and providing regular air changes in the operative and non-operative dental healthcare settings. Precautionary Principle-based measures are implementable when patients with active pulmonary tuberculosis are routinely treated.

Introduction

Tuberculosis, the oldest existing infectious disease

Mycobacterium tuberculosis is the oldest existing human pathogen, emerged 60,000–70,000 years ago. Tuberculosis (TB) dissemination, however, occurred 10,000 years ago during the Neolithic demographic transition, when animal domestication and agricultural innovations supported higher population densities, which maximized the human transmission cycle and reduced the likelihood of pathogen extinction through the exhaustion of susceptible hosts. Indeed, TB is a “crowd diseases” promoted by high population density. The Great White Plague, the first modern TB epidemic, took off in the late 1700s during the Industrial Revolution in the European and North-American cities, where poverty, overcrowding and malnutrition created an ideal environment for the spread of this disease. Nowadays, with 8.7 million new/relapse infections and 1.4 million deaths TB continues to be a major health problem worldwide. The distribution of the disease, however, is not uniform and is once again due to poverty, malnutrition and overcrowding. Indeed, 85% global cases occur in the Asian and African regions and 80% deaths in the African and South-East Asian regions, one third of all deaths occur among HIV-infected individuals .

TB transmission generally occurs when the microorganism is aerosolized by persons with active pulmonary TB disease during productive coughing and, occasionally, through sneezing, shouting and speaking. M. tuberculosis is carried through airborne particles, called droplet nuclei. These are droplets lower than 50 μm in size released in the environment and rapidly desiccated. Droplet nuclei are 1–5 μm in size and remain suspended in air for hours. The probability of a person exposed to M. tuberculosis to become infected depends on the concentration of infectious droplet nuclei in the confined space, the time passed in that space, inadequate air ventilation or recirculation and poor general health status .

After the initial TB infection (primary TB), the immune response may eradicate M. tuberculosis before symptom onset or the infection may progress and the individual develops active TB with pulmonary or extra-pulmonary symptoms, such as productive cough, night sweats, fatigue, malaise, fever and weight loss. Alternatively, the immune response may prevent further M. tuberculosis multiplication and spread and the subject does not develop the active disease, but bacteria remain alive in lungs or other organs for years. This condition is the latent TB infection (LTBI). 5% individuals with LTBI develop active TB later in life in consequence of immune depression, generally due to AIDS or malnutrition .

LTBI is diagnosed using the reactive tuberculin skin test (Mantoux or Tine tests – TST), which, however, yields false positive results due to either vaccination with the Bacille de Calmette et Guerin (BCG), or infection with non-tuberculous mycobacteria (NTM). Other tests are available which measure blood interferon gamma release (INF-γ release assay – IGRA) in response to TB-specific antigens, which are absent in BCG vaccinated and do not cross-react with the majority of NTM . Definitive LTBI diagnosis, however, is not possible because both TST and IGRA are designed to identify the adaptive immune response against M. tuberculosis , but cannot detect live mycobacteria . LTBI frequency is, therefore, overestimated because TST and IGRA cannot distinguish between eradicated TB infection and LTBI. In addition, since BCG vaccinated are TST positive LTBI overestimation is even greater using TST.

Tuberculosis among healthcare workers

The TB facts on Healthcare Workers (HCWs) vary according to the evaluation method. Indeed, studies are based on active pulmonary TB, M. tuberculosis infection, TST and/or IGRA conversion or prevalence. In 2012, in the WHO European Region, 340,000–390,000 new cases were diagnosed among HCWs and the annual incidence, prevalence and mortality rates were 40 (the second lowest after the American Region), 56 and 3.9 per 100,000, respectively. The number of smear-positive individuals (i.e., M. tuberculosi s detected in sputum at a level of 5000 or more microorganisms per mL), who are contagious, was relatively low (78,000). However, HCW immigrants from highly endemic areas, where incidence rates are as high as 200 per 100,000, are increasing .

Occupational risk among HCWs reflects both the microorganism circulation in the community and the occupation-related level of exposure in the healthcare settings. Therefore, the complete elimination of the occupational risk, particularly in endemic areas, is unrealistic and a more rational objective is the risk reduction to a level similar to the risk in the general population , a concept known as acceptable risk .

The advent of IGRA-based studies revealed that LTBI prevalence was lower than expected and non-occupational risk factors were prevailing on occupational factors. The main occupational risk factors among HCWs are associated with work locations likely attended by patients with active TB, such as inpatient TB facility, laboratory, internal medicine, emergency facilities, and with occupational categories, that is, radiology/laboratory technicians, patient attendants, nurses, ward attendants, paramedics and clinical officers . As a rule of thumb, the HCWs’ occupational risk is high in hospitals or settings with fewer than ten HCWs per admission for TB per year and low with more than one hundred HCWs per admission for TB per year .

Background and aim of the study

The dental environment is not considered at high TB risk by reviews focusing on all healthcare settings, except when patients with active TB are routinely treated . In contrast, the majority of reviews focusing on dentistry (references are only examples) report, with few authoritative exceptions , that TB risk in dental healthcare settings is relatively high. In addition, and in contrast with reviews reporting minimal TB risk among dental HCWs (DHCWs), many of the reviews reporting that DHCWs are at TB risk have been published by dental journals and are, therefore, more frequently read by DHCWs, who could be unnecessarily distressed.

The aim of this review was, therefore, to shed light on the actual risk of TB transmission in dental healthcare settings using the existing information.

Materials and methods

Literature search was performed to identify original papers concerning the risk of TB transmission among dental patients and DHCWs. Databases were PubMed, Scopus and GOOGLE Scholar. The keywords “tuberculosis” and “ Mycobacterium tuberculosis ” were matched with the keywords “dentistry”, “dentist”, “dental”, “dent*”, present in title/abstract (PubMed) title/keywords/abstract (Scopus), title and everywhere in the article (GOOGLE Scholar). There were no limitations regarding publication year and language, provided that abstracts were written in English and data could be extracted from tables. Generic keywords and broad databanks have been used to minimize the degree of selection bias, which refers to undetected published studies.

Inclusion criteria were that: (1) papers reported original data; eligible studies were observational studies, epidemiological surveillance reports, case reports/series, questionnaire-based surveys; (2) papers regarded dental healthcare settings, staff, patients; (3) information about any kind of TB-infection-related issue was reported. Exclusion criteria were that: (1) papers, such as reviews and editorials, did not report original data; (2) studies did not report TB-infection-related issues, such as studies on environmental contamination by M. tuberculosis (these studies have been used for the discussion and the evaluation of TB risk in dental healthcare settings); (3) studies reported original data but it was not possible to extract specific information regarding DHCWs and dental patients.

All titles, abstracts and tables were screened for an initial evaluation. Studies falling within the inclusion criteria were selected and split into studies about TB risk among dental patients and studies about the occupational risk among DHCWs. In some cases, the same study was considered for both purposes.

TB risk in dental healthcare settings has been differently conceptualized and studied by various scientific groups. It can be anticipated that few (if any) studies reported TB risk estimates. Indeed, study types ranged from case series, to macro-epidemiological surveillance studies reporting nation-based data. In addition, the geographical and historical contexts, where these studies were performed, were largely varying. Thus, in order to obtain a comprehensive idea of M. tuberculosis infection transmission in dentistry, the meta-narrative review was preferred to the more formal meta-analysis. Indeed, unlike meta-analyses, meta-narrative reviews include studies that may differ in type and structure and may have wide geographical and historical ranges, thus ensuring principles such as pluralism, pragmatism and historicity and the TB risk in dental healthcare settings emerged after the discussion of the papers included in the review. This study followed the RAMESES publication standards for meta-narrative reviews .

According to the style of narrative reviews, results were reported following a historical order, which accounted for the changing face of TB epidemiology, due to the globally improved well-being after WWII, the advent of effective antimicrobials and the implementation of TB control methods. Results also followed a geographical/ethnicity order, accounting for the different levels of overall health among developing and highly developed countries. Indeed, in the US and the UK, incidence rates among foreign-born persons were more than 10 times higher .

When necessary, proportions were extracted or calculated (e.g., TST conversion rates, TB incidence rates, proportions attributable to DHCWs, etc.) and 95% confidence intervals corrected for continuity were calculated accounting for zero values . The Website for Statistical Computation VassarStat (available at, vassarstats.net/last accessed October 12, 2015) was used.

Materials and methods

Literature search was performed to identify original papers concerning the risk of TB transmission among dental patients and DHCWs. Databases were PubMed, Scopus and GOOGLE Scholar. The keywords “tuberculosis” and “ Mycobacterium tuberculosis ” were matched with the keywords “dentistry”, “dentist”, “dental”, “dent*”, present in title/abstract (PubMed) title/keywords/abstract (Scopus), title and everywhere in the article (GOOGLE Scholar). There were no limitations regarding publication year and language, provided that abstracts were written in English and data could be extracted from tables. Generic keywords and broad databanks have been used to minimize the degree of selection bias, which refers to undetected published studies.

Inclusion criteria were that: (1) papers reported original data; eligible studies were observational studies, epidemiological surveillance reports, case reports/series, questionnaire-based surveys; (2) papers regarded dental healthcare settings, staff, patients; (3) information about any kind of TB-infection-related issue was reported. Exclusion criteria were that: (1) papers, such as reviews and editorials, did not report original data; (2) studies did not report TB-infection-related issues, such as studies on environmental contamination by M. tuberculosis (these studies have been used for the discussion and the evaluation of TB risk in dental healthcare settings); (3) studies reported original data but it was not possible to extract specific information regarding DHCWs and dental patients.

All titles, abstracts and tables were screened for an initial evaluation. Studies falling within the inclusion criteria were selected and split into studies about TB risk among dental patients and studies about the occupational risk among DHCWs. In some cases, the same study was considered for both purposes.

TB risk in dental healthcare settings has been differently conceptualized and studied by various scientific groups. It can be anticipated that few (if any) studies reported TB risk estimates. Indeed, study types ranged from case series, to macro-epidemiological surveillance studies reporting nation-based data. In addition, the geographical and historical contexts, where these studies were performed, were largely varying. Thus, in order to obtain a comprehensive idea of M. tuberculosis infection transmission in dentistry, the meta-narrative review was preferred to the more formal meta-analysis. Indeed, unlike meta-analyses, meta-narrative reviews include studies that may differ in type and structure and may have wide geographical and historical ranges, thus ensuring principles such as pluralism, pragmatism and historicity and the TB risk in dental healthcare settings emerged after the discussion of the papers included in the review. This study followed the RAMESES publication standards for meta-narrative reviews .

According to the style of narrative reviews, results were reported following a historical order, which accounted for the changing face of TB epidemiology, due to the globally improved well-being after WWII, the advent of effective antimicrobials and the implementation of TB control methods. Results also followed a geographical/ethnicity order, accounting for the different levels of overall health among developing and highly developed countries. Indeed, in the US and the UK, incidence rates among foreign-born persons were more than 10 times higher .

When necessary, proportions were extracted or calculated (e.g., TST conversion rates, TB incidence rates, proportions attributable to DHCWs, etc.) and 95% confidence intervals corrected for continuity were calculated accounting for zero values . The Website for Statistical Computation VassarStat (available at, vassarstats.net/last accessed October 12, 2015) was used.

Results

Primary study identification

The details of literature search are displayed in Fig. 1 . There were nineteen relevant studies, nine about transmission to patients and thirteen about occupational risk among DHCWs . Three studies were included in both categories.

Fig. 1
Flow chart of study search (last updated September 30, 2015).

Tuberculosis transmission to dental patients

Studies are displayed in Table 1 . The majority of editorials, reviews and studies claiming that the risk of TB transmission in dentistry is high , refer to the case series that occurred in 1979 . In the dental offices where an English dentist with active bilateral pulmonary TB was practicing, 15 of the 1084 dental patients who underwent dental extractions resulted infected with M. tuberculosis (presumptive transmission rate 1.4%). Fourteen of these infections occurred in the surgical site, involved cervical lymph-nodes and were explained by the direct contact of the extraction site by the dentist’s contaminated hands, since the dentist did not routinely wear gloves. Three of the 15 patients developed pulmonary TB (presumptive transmission rate, 0.3%) perhaps transmitted by droplet nuclei emitted by the dentist while performing the extractions, because the DHCW did not routinely wear a surgical mask. The Authors reported that TB clusters were common at that time in the UK and cited an example of a 13-year-old girl who transmitted pulmonary TB to 24 of 423 schoolmates, with a presumptive transmission rate of 5.7%, almost 20 times higher than the rate reported among dental patients. This episode cannot be transferred from the historical context where it occurred to the present time, since present-day dentists usually follow the basic infection control measures released by the Centers for Disease Control and Prevention (CDC), wear gloves and surgical masks and provide adequate air changes into the operative rooms . Indeed, TB clusters, such as those that happened in 1979, are actually very uncommon in the UK .

Table 1
Studies about TB infection among dental patients potentially associable to oral/dental healthcare.
First Author, Year Country Year of the survey Setting Outcome Sample Results Notes
Smith, 1982 UK 1979–1980 Dental patients who underwent dental extractions performed by a dentist with active lung TB Active TB 1084 tested for active TB plus 11 subjects who referred to the Nottingham Hospital (N = 1095) Active TB 1.4% (95 CI, 0.8–2.3%); active pulmonary TB 0.3% (95CI, 0.1–0.9%)
Lo Bello, 1984 Italy 1980 Two dental patients who underwent dental extractions Presumptive oral TB M. tuberculosis was not detected, presumptive diagnosis was histological None of the dental staff had active TB
Cleveland, 1995 US 1990 Dental patients exposed to two DHCWs with active lung TB in an HIV dental clinic Active TB due to the same isolate as that isolated from the two DHCWs 472HIV positive patients 0.0% (95 CI, 0.0–1.0%)
Selimoğlu, 1995 Turkey 1995 One dental patient who underwent dental extraction Presumptive pharyngeal TB M. tuberculosis was not detected, presumptive diagnosis was histological None of the dental staff had active TB
Anonymous, 1999 UK 1999 Dental patients exposed to dentist with active lung TB Active TB development during the infectivity period >450 (60 children) 0.0% (95 CI,0.0–1.1%)
Kawasaki, 2005 Japan 2001 Dental patients exposed to dentist with active lung TB TST positivity (Mantoux reaction); active TB development 132 TST positivity 6.8% (95 CI, 3.4–12.9%); active TB 0.0% (95 CI, 0.0–3.5%)
Cengiz, 2011 Turkey 2011 One dental patient who underwent dental extractions Confirmed oral TB None of the dental staff had active TB
Merte, 2014 US 2010 Dental patients exposed to dental hygienist with active lung TB TST positivity (Mantoux reaction); active TB development 305 TST positivity 7.5% (95 CI, 5.1–11.1%); active TB 0.0% (95 CI, 0.0–1.6%)
Mugang, 2014 UK 2010 Dental patients attending a dental hospital where a dental nurse with active TB was active active TB development Not reported None of direct-care patients was infected. One patient, one accompanying person, one DHCW who attended the hospital developed active TB Transmission was confirmed but occurred in another setting different from the operative rooms and was not healthcare associated
95 CI, 95% confidence interval.
When none of the dental staff has active TB, transmission due to DHCWs is unlikely.
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Jun 19, 2018 | Posted by in General Dentistry | Comments Off on Tuberculosis: Occupational risk among dental healthcare workers and risk for infection among dental patients. A meta-narrative review
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