Associate Professor Claire Dendle Infectious diseases physician and director of the infection and immunity service at Monash Health, Melbourne, Victoria.

First published online on 19 July 2024

BACKGROUND

LATENT TB infection is estimated

to be present in 5 % of the Australian population. 1 About 500,000 people in Australia are severely immunocompromised, with substantially more mildly or moderately immunocompromised. 2 Based on US data, it is probable the prevalence of immunosuppression in Australia is between 1.8 % and 3.1 %. 3 Therefore, a significant proportion of the Australian population is immunocompromised and requires screening and / or treatment for latent TB infection( LTBI).

In most patients, the host immune response controls TB, which results in the bacilli being enclosed in granulomata( see figure 1), leading to LTBI. 4

Patients with LTBI are at risk of progressing to active TB during the course of their lifetime. This risk is substantially increased when a patient is immunocompromised. A comparison of the features of LTBI and active TB infection is depicted in figure 2.

Most people with LTBI are unaware they have been exposed. Identifying

immunocompromised patients with LTBI and providing them with preventive treatment can substantially reduce the risk of active TB. Screening for LTBI may not be comprehensive in immunocompromised patients. 5

In Australia, LTBI management is shared across primary care; specialist hospital-based clinics; and community clinics, such as those specifically for refugee populations. Guidelines and review articles are available; however, considering the large number of immunocompromised patients in Australia and that access to specialist care can be challenging, patients may need to undertake management of their LTBI in a primary care setting. 6-10

This How to Treat explores the screening and management of LTBI in immunocompromised patients and aims to ensure GPs can decide which patient requires screening, how to implement preventive treatment, and suggestions about when to refer to an infectious diseases specialist.

SCREENING FOR LTBI

SCREENING for and management

of LTBI in immunocompromised patients involve a number of steps. These include interpreting testing, balancing the risk of reactivation of LTBI with the risk of drug toxicities and selecting the most appropriate preventive treatment( see figure 3).

Indications for screening

There are several international and

Australian guidelines that make recommendations regarding the groups of immunocompromised patients in whom screening is indicated. 7, 11

Figure 4 illustrates the author’ s approach to screening immunocompromised patients for LTBI. 7, 11

Timing of screening

It is optimal to perform screening

before initiation of immunosuppression. This is to increase the sensitivity of screening tests and to allow for initiation of preventive treatment before immunosuppression

starts. However, in practice, screening may only be performed after the patient is already immunosuppressed. This could be because screening has been overlooked or the patient’ s clinical circumstances may have worsened and an escalation of immunosuppression is required. Screening for LTBI can be performed at any point in a patient’ s immunosuppression journey.

Immunocompromised patients who have new epidemiological exposure to TB, such as a close contact or travel / residence in an endemic area, require screening or rescreening.

Diagnostic screening tests

Making a diagnosis of LTBI is complex

. There are epidemiological, radiological and immunological methods used to diagnose infection( see figure 5), none of which has high sensitivity or specificity in immunocompromised patients. In addition, concordance between these methods is imperfect.