Early Detection of Tuberculosis Outbreaks among the San Francisco Homeless: Trade-Offs Between Spatial Resolution and Temporal Scale

BACKGROUND: San Francisco has the highest rate of tuberculosis (TB) in the U.S. with recurrent outbreaks among the homeless and marginally housed. It has been shown for syndromic data that when exact geographic coordinates of individual patients are used as the spatial base for outbreak detection, higher detection rates and accuracy are achieved compared to when data are aggregated into administrative regions such as zip codes and census tracts. We examine the effect of varying the spatial resolution in the TB data within the San Francisco homeless population on detection sensitivity, timeliness, and the amount of historical data needed to achieve better performance measures. METHODS AND FINDINGS: We apply a variation of space-time permutation scan statistic to the TB data in which a patient's location is either represented by its exact coordinates or by the centroid of its census tract. We show that the detection sensitivity and timeliness of the method generally improve when exact locations are used to identify real TB outbreaks. When outbreaks are simulated, while the detection timeliness is consistently improved when exact coordinates are used, the detection sensitivity varies depending on the size of the spatial scanning window and the number of tracts in which cases are simulated. Finally, we show that when exact locations are used, smaller amount of historical data is required for training the model. CONCLUSION: Systematic characterization of the spatio-temporal distribution of TB cases can widely benefit real time surveillance and guide public health investigations of TB outbreaks as to what level of spatial resolution results in improved detection sensitivity and timeliness. Trading higher spatial resolution for better performance is ultimately a tradeoff between maintaining patient confidentiality and improving public health when sharing data. Understanding such tradeoffs is critical to managing the complex interplay between public policy and public health. This study is a step forward in this direction

Cost-effectiveness of tuberculosis evaluation and treatment of newly-arrived immigrants

BACKGROUND: Immigrants to the U.S. are required to undergo overseas screening for tuberculosis (TB), but the value of evaluation and treatment following entry to the U.S. is not well understood. We determined the cost-effectiveness of domestic follow-up of immigrants identified as tuberculosis suspects through overseas screening. METHODS: Using a stochastic simulation for tuberculosis reactivation, transmission, and follow-up for a hypothetical cohort of 1000 individuals, we calculated the incremental cost-effectiveness of follow-up and evaluation interventions. We utilized published literature, California Reports of Verified Cases of Tuberculosis (RVCTs), demographic estimates from the California Department of Finance, Medicare reimbursement, and Medi-Cal reimbursement rates. Our target population was legal immigrants to the United States, our time horizon is twenty years, and our perspective was that of all domestic health-care payers. We examined the intervention to offer latent tuberculosis therapy to infected individuals, to increase the yield of domestic evaluation, and to increase the starting and completion rates of LTBI therapy with INH (isoniazid). Our outcome measures were the number of cases averted, the number of deaths averted, the incremental dollar cost (year 2004), and the number of quality-adjusted life-years saved. RESULTS: Domestic follow-up of B-notification patients, including LTBI treatment for latently infected individuals, is highly cost-effective, and at times, cost-saving. B-notification follow-up in California would reduce the number of new tuberculosis cases by about 6–26 per year (out of a total of approximately 3000). Sensitivity analysis revealed that domestic follow-up remains cost-effective when the hepatitis rates due to INH therapy are over fifteen times our best estimates, when at least 0.4 percent of patients have active disease and when hospitalization of cases detected through domestic follow-up is no less likely than hospitalization of passively detected cases. CONCLUSION: While the current immigration screening program is unlikely to result in a large change in case rates, domestic follow-up of B-notification patients, including LTBI treatment, is highly cost-effective. If as many as three percent of screened individuals have active TB, and early detection reduces the rate of hospitalization, net savings may be expected

LM. Early detection of tuberculosis outbreaks among the San Francisco homeless: trade-offs between spatial resolution and temporal scale. PLOS One

Background San Francisco has the highest rate of tuberculosis (TB) in the US. Exact locations of patients' primary residences at the time of diagnoses are routinely collected as part of the TB surveillance program. It has been shown for syndromic surveillance data that when exact geographic coordinates of individual patients are used, higher detection rates and accuracy are achieved compared to when data are aggregated into administrative regions such as zip codes and census tracts. Here, we examine the effect of varying the spatial resolution in the TB data on the San Francisco homeless population, on detection sensitivity, timeliness, and the amount of historical data needed to achieve better performance measures. Methods and Findings We apply a variation of space-time permutation scan statistic to the TB data in which a patient location is either represented by its exact longitude and latitude or by the centroid of its census tract. We show that the detection sensitivity and timeliness of the method generally improve when exact locations are used to identify both simulated and real TB outbreaks, however, better performance measures were attained under simulated cases as compared to actual outbreaks. Finally, we compare the dependency of the method on the extent of data needed for parameter estimations under different geospatial constraints, and show that smaller amount of data is required when exact locations are used to achieve similar performance measures. Conclusion We investigate the relationship between using exact locations of TB patients, the timeliness of identifying real TB outbreaks, and the amount of legacy data required for early detection. We demonstrate that using higher spatial resolution results in higher detection rate, but more importantly in timely detection of TB outbreaks even when the amount of available data is relatively small. For higher spatial resolution, we also show generally better sensitivity for simulated outbreaks as compared to actual outbreaks, though this difference can be explained by the variations in dispersal structure of cases between the two. Trading higher spatial resolution for better performance, however, is ultimately a tradeoff between maintaining patient confidentiality and improving public health. Understanding such tradeoffs is critical to managing the complex interplay between public policy and public health. This study is a step forward in this direction

Pyrazinamide resistance, Mycobacterium tuberculosis lineage and treatment outcomes in San Francisco, California

Background: Pyrazinamide (PZA) is a first line agent for the treatment of active tuberculosis. PZA is also considered a potent companion drug for newer regimens under development. There are limited data on the demographic, clinical, and pathogen character

Association between diabetes mellitus and tuberculosis in United States-Born and foreign-born populations in San Francisco

© 2014 Suwanpimolkul et al.Setting: The impact of diabetes on tuberculosis in United States and foreign-born populations in San Francisco has not been studied. Objective: To determine the characteristics, prevalence and temporal trends of diabetes in US a

Tuberculosis progression rates in U.S. Immigrants following screening with interferon-gamma release assays

© 2016 The Author(s).Background: Interferon-gamma release assays may be used as an alternative to the tuberculin skin test for detection of M. tuberculosis infection. However, the risk of active tuberculosis disease following screening using interferon-ga

Tuberculosis progression rates in U.S. Immigrants following screening with interferon-gamma release assays

© 2016 The Author(s).Background: Interferon-gamma release assays may be used as an alternative to the tuberculin skin test for detection of M. tuberculosis infection. However, the risk of active tuberculosis disease following screening using interferon-ga

A Public Health Framework for Developing Local Preventive Services Guidelines

In this article, we describe the San Francisco Department of Public Health's (SFDPH's) framework for developing evidence-based screening and vaccination recommendations. We first reviewed our local data using surveillance and syndemic data. We then compiled and compared existing federal, state, and local recommendations. Then we identified differences as compared with our local evidence; where more evidence was required to make a recommendation, we culled from additional data sources and conducted additional analyses. Lastly, we developed our guidelines by confirming existing recommendations or making new recommendations based on this process. In the end, we successfully developed evidence-based clinical screening and prevention guidelines that have been adopted by the SFDPH Health Commission. We encourage the use of this framework in other public health settings at the local level

Tuberculosis progression rates in U.S. Immigrants following screening with interferon-gamma release assays

Abstract Background Interferon-gamma release assays may be used as an alternative to the tuberculin skin test for detection of M. tuberculosis infection. However, the risk of active tuberculosis disease following screening using interferon-gamma release assays in immigrants is not well defined. To address these uncertainties, we determined the incidence rates of active tuberculosis disease in a cohort of high-risk immigrants with Class B TB screened with interferon-gamma release assays (IGRAs) upon arrival in the United States. Methods Using a retrospective cohort design, we enrolled recent U.S. immigrants with Class B TB who were screened with an IGRA (QuantiFERON ® Gold or Gold In-Tube Assay) at the San Francisco Department of Public Health Tuberculosis Control Clinic from January 2005 through December 2010. We reviewed records from the Tuberculosis Control Patient Management Database and from the California Department of Public Health Tuberculosis Case Registry to determine incident cases of active tuberculosis disease through February 2015. Results Of 1233 eligible immigrants with IGRA screening at baseline, 81 (6.6 %) were diagnosed with active tuberculosis disease as a result of their initial evaluation. Of the remaining 1152 participants without active tuberculosis disease at baseline, 513 tested IGRA-positive and 639 tested IGRA-negative. Seven participants developed incident active tuberculosis disease over 7730 person-years of follow-up, for an incidence rate of 91 per 100,000 person-years (95 % CI 43–190). Five IGRA-positive and two IGRA-negative participants developed active tuberculosis disease (incidence rates 139 per 100,000 person-years (95 % CI 58–335) and 48 per 100,000 person-years (95 % CI 12–193), respectively) for an unadjusted incidence rate ratio of 2.9 (95 % CI 0.5–30, p = 0.21). IGRA test results had a negative predictive value of 99.7 % but a positive predictive value of only 0.97 %. Conclusions Among high-risk immigrants without active tuberculosis disease at the time of entry into the United States, risk of progression to active tuberculosis disease was higher in IGRA-positive participants compared with IGRA-negative participants. However, these findings did not reach statistical significance, and a positive IGRA at enrollment had a poor predictive value for progressing to active tuberculosis disease. Additional research is needed to identify biomarkers and develop clinical algorithms that can better predict progression to active tuberculosis disease among U.S. immigrants

Impact of GeneXpert MTB/RIF on patients and tuberculosis programs in a low-burden setting. a hypothetical trial.

RationaleGuidelines recommend routine nucleic-acid amplification testing in patients with presumed tuberculosis (TB), but these tests have not been widely adopted. GeneXpert MTB/RIF (Xpert), a novel, semiautomated TB nucleic-acid amplification test, has renewed interest in this technology, but data from low-burden countries are limited.ObjectivesWe sought to estimate Xpert's potential clinical and public health impact on empiric treatment, contact investigation, and housing in patients undergoing TB evaluation.MethodsWe performed a prospective, cross-sectional study with 2-month follow-up comparing Xpert with standard strategies for evaluating outpatients for active pulmonary TB at the San Francisco Department of Public Health TB Clinic between May 2010 and June 2011. We calculated the diagnostic accuracy of standard algorithms for initial empiric TB treatment, contact investigation, and housing in reference to three Mycobacterium tuberculosis sputum cultures, as compared with that of a single sputum Xpert test. We estimated the incremental diagnostic value of Xpert, and the hypothetical reductions in unnecessary treatment, contact investigation, and housing if Xpert were adopted to guide management decisions.Measurements and main resultsA total of 156 patients underwent Xpert testing. Fifty-nine (38%) received empiric TB treatment. Thirteen (8%) had culture-positive TB. Xpert-guided management would have hypothetically decreased overtreatment by 94%, eliminating a median of 44 overtreatment days (interquartile range, 43-47) per patient and 2,169 total overtreatment days (95% confidence interval, 1,938-2,400) annually, without reducing early detection of TB patients. We projected similar benefits for contact investigation and housing.ConclusionsXpert could greatly reduce the frequency and impact of unnecessary empiric treatment, contact investigation, and housing, providing substantial patient and programmatic benefits if used in management decisions