The most striking finding in our study is the high incidence of hospital admission for drug-resistant tuberculosis among HCWs in KZN, South Africa. HCWs were found to have a 5 to 6 fold increased rate of hospital admission with MDR-TB or XDR-TB compared with non-HCWs. This burden of disease is particularly concerning since HCWs are also front line care providers for TB and HIV patients in the province.
The higher rate of hospitalization for drug-resistant TB among HCWs in our study was not explained by higher percentages of HIV infection or previous TB treatment among HCWs compared to non-HCWs. It is likely that the increased risk for HCWs seen in our study is due to increased occupational exposure to drug-resistant MTB within health care settings. (20
) The majority of HCWs with MDR-TB and XDR-TB were young, female, with a significant burden of HIV-infection, reflecting the epidemiology of the HIV epidemic in KZN (21
). Female nurses are known to be a high-risk group for nosocomial TB (4
) because of their close and prolonged risk of contact with TB patients, and it is plausible that many young females in our HCW cohort were nurses or nursing trainees.
In South Africa, XDR-TB/HIV co-infection was highlighted by the well-publicized 2006 outbreak at Tugela Ferry, KZN (10
). The authors raised the concern that the XDR-TB outbreak was nosocomial, and therefore South African HCWs could be at high risk for primary acquisition of XDR-TB (20
). Although we lack molecular epidemiologic data on TB isolates, we assume that many of the drug-resistant-TB cases among HCWs reported in our study represent primary drug-resistant TB. This assumption is supported by the fact that HCWs in our study were less likely to report previous TB treatment compared to non-HCWs, and is consistent with other studies of risk for drug-susceptible TB among HCWs in Africa (3
). From an infection control standpoint, it is important to note that the majority of HCWs with MDR-TB and XDR-TB were referred from, and may have worked at, non-TB specialist facilities. This implies that it is not enough to focus infection control efforts at specialist TB hospitals in South Africa in order to prevent nosocomial transmission of drug-resistant TB.
Drug-resistant TB among health care workers in the developing world has been underreported. To date, there has been one published case report of a single health care worker infected with nosocomial XDR-TB in India (23
). In reports from the U.S. in the 1990s there have been case series reporting nosocomial MDR-TB transmission to HCWs in hospital (5
), a dental clinic (24
) and HIV/AIDS hospital wards (6
). The increased risk for XDR-TB and MDR-TB hospitalization we report is similar in magnitude to the estimated increased risk for drug-susceptible TB among HCWs in a hospital based study (25
) and in a systematic review of TB risk for HCWs in low income countries (26
). The elevated risk for XDR-TB among HCWs is a critical public health concern because of low cure rates, increased mortality, and potential nosocomial transmission to patients and other HCWs (25
). The high proportion of HIV co-infection we observed in HCWs admitted for initiation of TB therapy is particularly alarming as in two recent studies approximately 40% of HIV and XDR-TB co-infected patients died within 12 months of therapy, and only 18 – 20% achieved culture conversion (11
Our study has several limitations many of which reflect challenges in collecting retrospective data in resource-constrained settings. First, stigma may have prevented persons from seeking or accepting HIV testing (30
) therefore HIV status may be misclassified and/or underreported. Second, we lacked details regarding HCWs occupational classifications, and so could not identify degree or duration of exposure to drug-resistant TB. Third, HCWs with drug-resistant TB may have been more likely to obtain microbiologic diagnosis, seek specialized referral, or access treatment at KGV compared to non-HCWs leading to referral bias. For example, HCWs who were more likely to get ARVs may have been more likely to develop symptomatic TB (or immune reconstitution inflammatory syndrome) leading to increased TB diagnosis. On the other hand, HCWs are potentially less likely to seek care in a public health facility or self-identify as HCWs, leading to an underestimate of MDR-TB or XDR-TB hospitalization incidence. Fourth, the HCW workforce in KZN was estimated using professional registering bodies for professional workers and filled posts in the public health sector for non-professional workers (19
). This undercounted private sector non-professional HCWs and could lead to an overestimate of hospitalization rates drug-resistant TB among HCWs. On the other hand, the estimate may inflate the numbers of professional HCWs since registering bodies include HCWs who have retired, emigrated, died or who no longer work in the health care sector leading to an underestimate of rates (19
). Fifth, it is possible that patients may have come from other provinces in South Africa or other countries such as Leostho or Swaziland causing an overestimate in the numerator for population-based rate calculations. Given the large distances between treatment centers (several hundred miles) and known health-seeking patterns it is unlikely there was substantial misclassification of cases. Finally, to estimate the incidence of drug resistant TB the numerators of our reported rates are based on admission to a TB referral hospital rather than all diagnosed MDR-TB and XDR-TB in KZN. A recently published community-based study of MDR-TB and XDR-TB in KZN report nearly 50% 30 day mortality after collection of sputum and prior to admission for appropriate second line TB treatment. This suggests that our study of hospital admissions might underestimate the incidence of both MDR-TB and XDR-TB in KZN (31
Future research directions include identifying specific practices and occupational classifications that place HCWs at risk for drug-resistant TB. We are developing studies to identify obstacles to the implementation of best practices in infection control in KZN health care institutions.
The results of this study have implications for health policy in countries with endemic HIV and drug-resistant tuberculosis. HCWs are likely at substantially higher risk for drug-resistant TB compared with the general population and this should be addressed by occupational risk reduction and infection control policy. A recently updated evidence-based guideline on TB infection control for HCWs in hospitals and congregate settings (26
) published in 2009 by the WHO recommends prioritizing TB control on the national level, including developing national infection control policies in member states, implementing administrative and environmental controls, implementing ongoing surveillance for TB disease among HCWs, monitoring and evaluating infection control measures, and conducting operational research. Policies that prioritize reducing HCWs occupational risk for drug-resistant TB are urgently needed to reduce the numbers of MDR-TB and XDR-TB infected HCWs and nosocomial transmission of drug-resistant TB in South Africa.