Abstract
The re-emergence of tuberculosis (TB) in the mid-1980s in many parts of the world, including the United States, is often attributed to the emergence and rapid spread of human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS). Although it is well established that TB transmission is particularly amplified in populations with high HIV prevalence, the epidemiology of interaction between TB and HIV is not well understood. This is partly due to the scarcity of HIV-related data, a consequence of the voluntary nature of HIV status reporting and testing, and partly due to current practices of screening high risk populations through separate surveillance programs for HIV and TB. The San Francisco Department of Public Health, TB Control Program, has been conducting active surveillance among the San Francisco high-risk populations since the early 1990s. We present extensive TB surveillance data on HIV and TB infection among the San Francisco homeless to investigate the association between the TB cases and their HIV+ contacts. We applied wavelet coherence and phase analyses to the TB surveillance data from January 1993 through December 2005, to establish and quantify statistical association and synchrony in the highly non-stationary and ostensibly non-periodic waves of TB cases and their HIV+ contacts in San Francisco. When stratified by homelessness, we found that the evolution of TB cases and their HIV+ contacts is highly coherent over time and locked in phase at a specific periodic scale among the San Francisco homeless, but no significant association was observed for the non-homeless. This study confirms the hypothesis that the dynamics of HIV and TB are significantly intertwined and that HIV is likely a key factor in the sustenance of TB transmission among the San Francisco homeless. The findings of this study underscore the importance of contact tracing in detection of HIV+ individuals that may otherwise remain undetected, and thus highlights the ever-increasing need for HIV-related data and an integrative approach to monitoring high-risk populations with respect to HIV and TB transmission.
Highlights
San Francisco has the highest rate of TB in the United States, nearly three to four times the national rate [1]
Data The dataset for this study consists of comprehensive information on individuals that have been diagnosed by the San Francisco Department of Public Health (SFDPH) TB Control Program (TBCP) with active TB (TB cases), and their reported contacts (PPD+ and PPD2), all identified from January 1993 to December 2005
Using extensive TB surveillance data on the San Francisco homeless, we found that the evolution of TB cases and their human immunodeficiency virus (HIV)+/PPD2 contacts is significantly interdependent, synchronized at about every 2.5 years and separated by the mean lag time of 5.4 months
Summary
San Francisco has the highest rate of TB in the United States, nearly three to four times the national rate [1]. While the number of TB cases has been steadily declining since the early 1990s in San Francisco’s general population exclusive of the homeless (non-homeless) (Figure 1A), the rate of decline has been much slower and more variable for the homeless population, in spite of extensive active surveillance among the homeless by the SFDPH TBCP (Figure 1B) This disparity in trends has been mostly attributed to the prevalence of HIV and AIDS among the indigent population in San Francisco [6,7], and in many impoverished regions of the world [8,9,10,11,12,13,14,15,16,17], few studies have been properly designed and documented to establish a direct epidemiological link between TB and HIV
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