Table 1.

Characteristics and limitation of the WHO TB patient cost survey and the adapted version for longitudinal studies in Africa

	Generic WHO TB patient cost survey	Adapted patient cost survey – for TB Sequel
Design	Cross-sectional facility-based	Longitudinal facility-based
Geographic location	National survey	Five African study clinics located in The Gambia, Mozambique, South Africa and Tanzania.
Population	All patients (adults and children) registered for TB (drug-susceptible or drug-resistant) treatment in the National Treatment Programme (NTP).	Adult patients (≥18 years) registered for TB (drug-susceptible or drug-resistant) treatment in the National Treatment Programme (NTP) in the study sites
Sampling	Random cluster sampling or a national simple random sampling where electronic registers are available.	Consecutive sampling – as eligible participants present at the facility [10]
	Sample size based on assumed prevalence of catastrophic costs.	Sample size based on prevalence (>20%) of the outcome of interest which is severe pulmonary function impairment, measured by spirometry at least 2 years after treatment initiation
Enrolment	Consecutive patients registered for TB treatment who are attending a sampled facility and are a minimum of 14 days into either the intensive or continuation phase.	Starting (+/- 14 days) TB treatment after TB diagnosis.
Interview schedule	Each patient is interviewed only once	Patients are interviewed multiple times at defined study visits (M0, M2, M6, M12 and M24).
Resources and time requirements	The survey team is typically comprised of a principal investigator, a survey coordinator, a data manager and interviewers – these are temporary or short-term positions.	The team composition includes data capturers, quality control manager, and a statistician. Permanent or long-term positions are needed for continuity and retention of experienced staff.
	Once off interview and consent (±45 minutes), either paper-based or electronic survey.	Multiple interviews (±45 minutes), only paper-based survey with data entry into an electronic database.
	Qualitative interviews can be performed both with patients and household members, as well as health and social service staff and policy-makers [2].	No qualitative component but includes additional component to study social consequences (e.g. quality of life, pain, disability and stigma related to TB) [10].
Interviewers	Facility-based	Facility- and community-based
Calculating total costs	Requires some retrospective data collection, forward projections and imputations to calculate the total costs.	Total costs available for each phase of TB treatment (i.e., pre-treatment, intensive phase of treatment, continuation phase of treatment and post-TB treatment).
	Only patients in the intensive phase receive questions on the costs incurred prior to diagnosis.	All patients receive questions on the costs incurred prior to diagnosis at the enrolment/M0 visit.
Outcomes	Treatment outcomes are typically not available	Treatment outcomes are available
	Estimate the cost per patient treated for TB	Can estimate the cost per patient treated for TB by outcome Repeated measures of health-related quality of life, pain, depression or anxiety and disability related to TB is collected at M2, M6, M12 and M24. May contribute to better estimates of disability-adjusted life years (DALYs).
Limitations	Survey findings can only be generalized to a subset of people with TB who receive care in the NTP. Conclusions cannot be drawn about all people with TB in the country.	Survey findings can only be generalized to a subset of people with TB who receive care in the NTP in the study sites. Conclusions cannot be drawn about all people with TB in the country.
		The study site may not necessarily be where the patient goes for routine TB care or to collect medication. This may result in issues with recall as participants try to distinguish between routine treatment versus study related visits.
		Direct costs, income loss or coping costs may be underestimated as study sites reimburse patients for travel and time at each visit or may provide support (e.g. food parcels, supplements, travel vouchers) to promote retention.
	Recall bias – a major challenge for the estimation of total patient costs incurred. This mainly affects cost estimates for the pre-treatment period.	To minimize recall bias, patients receive questions on the costs incurred prior to diagnosis at the first visit (M0). During subsequent visits, patients are asked to recall since the date of their last interview. Interviewers are also trained to make it easier for the patient to recall by using local methods of time structuring.
	Costs after treatment completion are not included.	Costs after treatment completion are included. Patients are followed for a minimum of 24 months after TB treatment initiation.
	The current methodology only includes TB patients enrolled and retained in care.	A longitudinal design can only consider earlier aspects of the cascade of care, prior to when a patient becomes lost to follow up.