To the Editor: We disagree with the recent recommendation of Graham and colleagues that all medical students should be offered BCG vaccination.1 In countries with a low prevalence of tuberculosis (TB), the side effects from the vaccine and losing the use of a Mantoux test to readily diagnose recent TB infection outweigh any benefits of a vaccine with relatively poor efficacy.

The incidence of pulmonary TB in Australia is low (3.3 per 100 000 per year) and only 1.5% of isolates are multidrug-resistant.2,3 Thus, the likely exposure of medical students and doctors in Australia to pulmonary TB (let alone multidrug-resistant TB) will be low. In addition, most hospitalised patients with pulmonary TB would have been suspected of having TB before being sent to hospital, so adequate respiratory precautions should have been in place for most. This makes the risk of transmission to health care workers very small.

Information from the Australian immunisation handbook is also very relevant to this debate.4 BCG can be effective, but mainly in preventing disseminated TB in children (> 80% efficacy). In adults, the overall protective efficacy is only about 50%,4 and the sole Australian study showed, at best, a protective efficacy of only 30%.5 The effect of BCG may not persist for more than 10 years but repeat vaccination is not recommended.4

Adverse events occur in about 5% of those vaccinated, with 2.5% being injection site abscesses and 1% lymphadenitis. About 1% of vaccinees may need medical attention as a result of the adverse event. Anaphylactoid reactions can occur, and keloid scarring can also occur (although rarely) at the injection site. The vaccine is “live”, and therefore contraindicated in anyone who might have HIV, other forms of immunosuppression, or generalised skin diseases.4

Graham and colleagues believe the problem of BCG vaccination interfering with the interpretation of Mantoux results can be overcome by using whole blood-based interferon assays, such as QuantiFERON-TB Gold, purportedly unaffected by BCG vaccination.1 However, the data for QuantiFERON-TB Gold need to be treated with some caution because it is a new test and there is no gold standard against which to compare it for diagnosing latent TB. The specificity of interferon assays in diagnosing latent TB has been estimated at 95% or more,6 but this will still result in a poor positive predictive value if the pretest probability of latent TB infection is low — and this is the case for health care workers in Australia.

In summary, Australia is far more likely to protect its health care workers from TB through effective hospital infection control measures and migrant screening than through a vaccination program with a mediocre vaccine.

To the Editor: Graham and colleagues correctly assert that medical students are at increased risk of infection with Mycobacterium tuberculosis in settings where they are treating patient groups with a high prevalence of active pulmonary tuberculosis (TB).1 This is well illustrated by the increasing prevalence of latent TB infection among medical students in their later clinical years in countries where community TB incidence markedly exceeds that of Australia.2

Their case for a standard approach to screening of medical students at course entry has great merit, and their arguments in favour of using an interferon gamma release assay to screen for latent TB infection would bring Australia into line with current international best practice.

However, the data presented do not substantiate a policy of offering BCG vaccination to all Australian medical students whose screening test result for latent TB infection, whether by interferon gamma or tuberculin skin testing (TST), is negative. Although BCG offers definite benefits in reducing the risk of life-threatening disseminated disease in children under 2 years of age, it does not offer dependable protection against pulmonary TB in adults.4 Medical students who are vaccinated with BCG may be lulled into a false sense of security, and neglect other more effective infection control measures that would reduce their risk of TB exposure and infection. Although BCG is a relatively safe vaccine, there is a small but well defined risk of local and systemic adverse events.5

We therefore support a standardised approach to screening medical students with TST or, preferably, interferon gamma at course entry and exit. Screening for latent TB infection should be offered whenever merited during the course of study, after exposure to active TB disease in Australia or abroad. The benefits of chemoprophylaxis on conversion outweigh the risks associated with isoniazid use, and the risks associated with BCG may not be acceptable where the risk of TB exposure for many Australian medical students is currently negligible.

In reply: The intention of our article was to highlight inconsistent approaches to tuberculosis (TB) prevention in Australian medical schools and stimulate a new informed debate. We therefore welcome the responses from Senanayake and Collignon, and Durrheim and Hensley.

Interference with interpretation of tuberculin skin testing (TST) is one argument cited against the use of BCG vaccination for health care workers. While we agree that the new blood-based tests need further evaluation, unlike TST, they are not affected by BCG because they employ TB-specific antigens. The lack of a gold standard for diagnosis of latent TB affects both TST and the blood-based tests. Recent reviews of these new tests have been favourable — including one that states that, compared with TST, these new assays seem to have “better correlation with surrogate measures of exposure to M. tuberculosis” and that “because of their higher specificity they may be helpful in low-prevalence, resource-rich settings where cross-reactivity due to BCG may pose difficulty in BCG interpretation”.1 In fact, this article summarised the specificity of these new tests as between 95% and 100%. Other authors found a specificity of 98.1%.2

We agree that infection control is crucial in preventing nosocomial TB transmission, but every infection control practitioner has seen patients with unrecognised TB admitted to an open ward. One missed patient can mean contact-tracing and testing of dozens of staff. The Melbourne Mantoux study (involving 14 Melbourne hospitals) found that health care work and years of hospital employment were significantly associated with a positive Mantoux result — indicating the risk to Australian health care workers is not “negligible” as Durrheim and Hensley state. Nosocomial outbreaks of TB are well documented in low-prevalence countries.1,3

BCG is by no means a perfect vaccine. However, while BCG efficacy was once thought to only last 10 years, a recent large study suggested that it persists for 50–60 years,4 and there is new evidence that BCG vaccination may prevent some primary infections.5 While the risk of health care-associated tuberculosis in Australia is currently low, it would be unwise to assume this will remain the case, or that doctors will only work in safe environments. What will be the effects of HIV, further immigration from high-risk countries, drug resistance and the increasing use of immunosuppressant medications on the incidence of TB? We stand by the recommendations in our article, although we acknowledge they are controversial. There should, however, be no controversy about the need for a consistent policy concerning TB prevention in our medical schools.