Patient Diagnostic Rate as Indicator of Tuberculosis Case Detection, South Africa

To address the uncertainty of the indirectly measured tuberculosis case detection rate, we used survey data stratified by HIV status to calculate the patient diagnostic rate, a directly measurable indicator, in 8 communities in South Africa. Rates were lower among HIV-negative than HIV-positive persons. Tuberculosis programs should focus on HIV-negative persons.


The Study
The 2010 ZAMSTAR survey measured prevalence of culture-positive TB after 3 years of interventions in communities with a high TB/HIV burden. We selected communities that had a TB notification rate of >400 cases/100,000 population/year, were served by a healthcare facility offering TB diagnosis and treatment, and had a catchment area of >25,000 persons. Standard census enumerator areas were randomly selected within communities, and all adults (>18 years of age) from all households within the selected areas were asked to participate.
After obtaining written informed consent, we collected 1 sputum sample from each adult and offered HIV testing with 2 rapid HIV tests (Determine HIV-1/2, Alere, San Diego, CA, USA; and Uni-Gold, Trinity Biotech, Bray, Ireland). Participants who self-reported themselves as HIV positive were asked to be retested, but if they refused, they were not tested and were assumed to be HIV positive. Sputum samples were inoculated onto manual mycobacterial growth indicator tubes (Becton Dickinson, Franklin Lakes, NJ, USA), and identification of Mycobacterium tuberculosis isolates was confirmed by 16SrRNA sequencing (4).
Community notification rates were determined by using 2010 notification data from the electronic TB register of the community facility for the number of all newly notified cases (numerator) and 2011 census data for the estimated population size (denominator). To estimate the number of persons living with HIV, we stratified notification rates by using HIV data from the TB register for notified cases and by splitting the population per community into HIV positive or negative according to prevalence survey HIV results (Table 1). Prevalence rates were standardized by age and sex according to the 2011 census age/sex distribution per community. Prevalence data were stratified by HIV by using a survey variable that captured HIV test results combined with self-reported HIV status (online Technical Appendix, http://wwwnc.cdc.gov/EID/article/22/3/15-1618-Techapp1.pdf). The PDR per community, stratified by HIV status, was calculated by dividing notification rate by prevalence (Table 2).
We assumed that the 2011 census would give an accurate estimate of the community population in 2010 and that the HIV prevalence in the community population would be similar to that in the survey population. We varied these assumptions according to estimated national population growth and national adult HIV prevalence in a sensitivity analysis; the effect was minimal (data not shown).
Overall, the PDR was 0.34 (95% CI 0.29-0.39) per person-year for the HIV-negative population and 1.53 (95% CI 1.27-1.79) per person-year for the HIV-positive population. In all 8 communities, the PDR was lower for the HIVnegative than the HIV-positive population (  transmission (10); efforts should include strategies to detect HIV-negative patients who might contribute proportionally more to community transmission (11) and be accessing healthcare services already (12). HIV-negative persons who are more likely to be smear positive should undergo diagnostic testing for TB; for TB-positive persons, effective treatment should be started quickly (13). Our findings should be validated with analyses from other settings. Given the current World Health Organization focus on prevalence surveys, data for such analyses should be available. To help TB programs to develop active case-finding strategies, future research could investigate HIV-negative persons who are at risk of having TB and being missed by the healthcare system.