Health needs are diverse, and programmes are expected to provide a range of diagnostics to assist health workers in managing patients. The diagnosis of TB often begins with symptom screening, which is not specific to TB, given that cough and fever overlap with COVID-19 and other respiratory infections. Additionally, people with TB may be coinfected with HIV, particularly in sub-Saharan Africa, and services for both diseases are usually provided at the same levels of care. The relative diagnostic volumes are also quite heterogeneous, and they can be low for a specific disease or on a specific day at peripheral health centres, justifying the need for multidisease testing using the same equipment. An information note describing considerations for multidisease testing is available (34).
All currently recommended molecular diagnostics for the initial diagnosis of TB have a SARSCoV-2 test available on the same platform as the TB test, although some may not have received regulatory approval for such use. Several platforms are widely used in diagnosing and managing PLHIV, whereas others are used for antimicrobial resistance detection of bacterial pathogens. NGS platforms can be used to sequence any nucleic acids present in a sample. The response to the COVID-19 pandemic led to NGS capacity being established in many countries, including lowand middle-income countries, for surveillance. Such capacity and expertise may be available and could be used to facilitate the rapid uptake of targeted NGS-based DST for TB. The decision to choose a particular test and brand would also need to consider the instruments available in a particular setting and the capacity to add TB testing. If multidisease testing on an instrument is planned, then it would be best to employ platforms that use random access approaches (e.g. GeneXpert) or allow different types of tests to be performed on the same batch (e.g. cobas, BD MAX or targeted NGS).
Multidisease testing has the advantage of shared financial costs for equipment purchasing and maintenance, as well as human resources. Efficiencies could also be achieved where multidisease testing results in optimal use of equipment and batch sizes; however, if it is not well planned (e.g. if a well-functioning collaboration between vertical disease programmes is not ensured), such testing could have the opposite effect. Equitable access and shared prioritization of testing are important to ensure that people with a particular disease are not disadvantaged. For example, the use of targeted NGS for clinical decision-making should be prioritized over its use for surveillance. The overall laboratory budgets should ensure fair distribution based on burden of disease and need.
Multidisease testing is mainly useful in settings where only a small number of tests are undertaken by individual programmes (e.g. the likely small numbers of people with DR-TB on a day-to-day basis that may require targeted NGS). In this scenario, prioritizing such samples in a run and “filling” the batch with SARS-CoV-2 or other surveillance samples may improve cost efficiency. In contrast, multidisease testing will be less relevant where there are large needs for TB and HIV testing and infrastructure is installed to meet the demand. Nonetheless, the burden of disease and testing volumes change over time; hence, the use of equipment should be monitored and programmes may need to adapt.