Table 2 Existing TB case-finding definitions and how they link to pathways in the model

Passive TB case finding

Patient-initiated pathway to TB diagnosis involving (1) a person with active TB experiencing symptoms that he or she recognizes as serious; (2) the person having access to and seeking care, and presenting spontaneously at an appropriate health facility; (3) a health worker correctly assessing that the person fulfils the criteria for suspected TB; and (4) the successful use of a diagnostic algorithm with sufficient sensitivity and specificity to diagnose TB [3]

Our model distinguishes two types of care-seeking pathways. TB diagnostic services with open invitation to people with TB symptoms (Fig. 2, black dashed pathway) reflect the patient-initiated pathway. In our model it differs from the general care-seeking pathway, where patients with TB symptoms are mixed with people seeking care for other health problems (Fig. 2, green dashed pathway)

Passive case finding with an element of systematic screening

Passive case finding may involve an element of systematic screening if identification of people with suspected TB is done systematically for all people seeking care in a health facility or clinic [3]

At general health services, screening could be conducted to identify patients with presumptive TB who did not seek care for TB symptoms specifically. TB screening of all people accessing care at general health services represents PCF with an element of systematic screening (Fig. 2, green solid pathway). However systematic screening for active TB cannot be conducted at TB diagnostic services with open invitation to people with TB symptoms, as this group is self-selected

A triage test for TB

A test that can be rapidly conducted among people presenting to a health facility to differentiate those who should have further diagnostic evaluation for TB from those who should undergo further investigation for non-TB diagnoses [23]

In the model, a triage test for TB is the same as a screening test for TB in people seeking care at general health services

Enhanced TB case finding

Uses health information or education, or awareness campaigns to provide information about what type of health-seeking behaviour is appropriate when people experience symptoms of TB; this type of case finding may be combined with improving access to diagnostic services. Enhanced case finding may or may not be combined with screening [5, 23]

TB health promotion to improve TB care seeking along care-seeking pathways meets the definition of ECF. From our model, it is evident that the information provided via these health promotion messages may not be sufficient in enhancing screening pathways, which include non-care-seeking pathways. Careful consideration should be given to the content of health promotion messages when ECF is combined with screening, especially when screening is conducted with a tool that is sensitive enough to identify preclinical disease, e.g. CXR. In this context, health information or education about risk and prevention of TB can enhance non-care-seeking pathways

Active TB case finding

Synonymous with systematic screening for active TB, although it normally implies screening that is implemented outside of health facilities [3]

This definition has recently been refined to the following: provider-initiated screening and testing in communities by mobile teams, often using mobile X-ray and rapid molecular tests. The term is sometimes used synonymously with systematic screening [23]

Dedicated TB screening services (Fig. 2, blue and orange pathways) reflect ACF. The target group could include a whole population or TB contacts (see TB contact investigation). Our model distinguishes between two types of dedicated TB screening services. The main distinguishing factor separating the two types is the availability of screening

TB screening personally offered to target group members at home, work or school (Fig. 2, orange pathway) bypasses access barriers and enhances the dedicated TB screening pathway

TB contact investigation

A systematic process for identifying previously undiagnosed people with TB disease and TB infection among the contacts of an index TB patient and/or other comparable settings where transmission occurs. Contact investigation consists of identification, clinical evaluation and/or testing and provision of appropriate anti-TB therapy (for people with confirmed TB) or TB preventive treatment (for those without TB disease) [8]

TB contact investigation does not imply a specific type of case-finding intervention. TB contacts may be invited to general health services or TB diagnostic services if they develop TB symptoms (care-seeking pathways). TB contacts may also be invited to dedicated TB screening services at a health facility or at their home (Fig. 2, blue and orange pathways)

Intensified TB case finding

WHO guidance for intensified TB case finding states, “All people living with HIV, wherever they receive care, should be regularly screened for TB using a clinical algorithm at every visit to a health facility or contact with a health worker.” [6]

Intensified case finding is represented by screening of PLHIV linked to care (Fig. 2, grey pathway). Of note, “HIV” can be replaced by any other “clinical risk group” and “HIV care” can be replaced by any other “risk group care”, e.g. screening of pregnant women linked to antenatal care