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Travis C Porco

Publications and source records attributed to Travis C Porco.

14 recordsLinked to original sources
PubMed2006

Assessing the validity of tuberculosis surveillance data in California.

BACKGROUND: The Centers for Disease Control and Prevention (CDC) convened a workgroup to revise the tuberculosis (TB) case report in the United States of America (U.S.). The group proposed substantial revisions. Study objectives were to systematically assess the validity and completeness of reported TB case surveillance data in California and to inform TB case report revision process. METHODS: A sample of 594 cases was retrospectively selected from the cohort of all TB cases reported during 6/1/96-5/31/97 to the State TB Registry. Cases, stratified by treatment outcome, were randomly sampled within each outcome category. Data for 53 variables were abstracted from each case's public health medical record and compared to data recorded on the TB case report. Using the medical record as the "gold standard," estimates were developed for 1) concordance, sensitivity, and positive predictive value of reported data for categorical variables; 2) the absolute mean difference between the two information source for date variables; and 3) the completeness of data on the case report and in medical record. RESULTS: At least 90% of the values for 35 (79.5%) categorical variables submitted on the TB case report form were identical to values in the medical record. Concordance between data on the case report and medical record was lower for the remaining nine (20.5%) categorical variables: status of abnormal chest x-ray (46.8%); directly observed therapy (48.6%); smear result for tissue or body fluid other than sputum (49.2%); type(s) of tissue or body fluid for smears and cultures other than sputum (76.4% and 73.9% respectively); provider type (73.4%); occupation (84.4%); sputum culture conversion (85.4%); and sputum smear result (89.6%). Case report data were more complete than data in the medical record; 2.9% versus 9.8% of data were missing/unknown, respectively. CONCLUSION: For most variables examined on the TB case report, data validity was excellent, indicating a robust surveillance system. However, lower data quality was noted for a small number of variables primarily impacting treatment adherence, including assessment and planning; advocacy; allocation and garnering of resources; and research. The study provides compelling evidence supporting the CDC workgroup's proposed revisions to the TB case report.

Body Fluids↗
PubMed2006

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.

Adult↗
PubMed2006

Prospects for advancing tuberculosis control efforts through novel therapies.

BACKGROUND: Development of new, effective, and affordable tuberculosis (TB) therapies has been identified as a critical priority for global TB control. As new candidates emerge from the global TB drug pipeline, the potential impacts of novel, shorter regimens on TB incidence and mortality have not yet been examined. METHODS AND FINDINGS: We used a mathematical model of TB to evaluate the expected benefits of shortening the duration of effective chemotherapy for active pulmonary TB. First, we considered general relationships between treatment duration and TB dynamics. Next, as a specific example, we calibrated the model to reflect the current situation in the South-East Asia region. We found that even with continued and rapid progress in scaling up the World Health Organization's DOTS strategy of directly observed, short-course chemotherapy, the benefits of reducing treatment duration would be substantial. Compared to a baseline of continuing DOTS coverage at current levels, and with currently available tools, a 2-mo regimen introduced by 2012 could prevent around 20% (range 13%-28%) of new cases and 25% (range 19%-29%) of TB deaths in South-East Asia between 2012 and 2030. If effective treatment with existing drugs expands rapidly, overall incremental benefits of shorter regimens would be lower, but would remain considerable (13% [range 8%-19%] and 19% [range 15%-23%] reductions in incidence and mortality, respectively, between 2012 and 2030). A ten-year delay in the introduction of new drugs would erase nearly three-fourths of the total expected benefits in this region through 2030. CONCLUSIONS: The introduction of new, shorter treatment regimens could dramatically accelerate the reductions in TB incidence and mortality that are expected under current regimens-with up to 2- or 3-fold increases in rates of decline if shorter regimens are accompanied by enhanced case detection. Continued progress in reducing the global TB burden will require a balanced approach to pursuing new technologies while promoting wider implementation of proven strategies.

Antitubercular Agents↗
PubMed2006

HIV drug-resistant strains as epidemiologic sentinels.

Observed declines in drug resistance to nucleoside reverse transcriptase inhibitors among persons recently infected with HIV-1 in monitored subpopulations can be interpreted as a positive sign and lead public health officials to decrease efforts towards HIV prevention. By means of a mathematical model, we identified 3 processes that can account for the observed decline: increase in high-risk behavior, decrease in proportion of acutely infected persons whose conditions are treated, and change in treatment efficacy. These processes, singly or in combination, can lead to increases or decreases in disease and drug-resistance prevalence in the general population. We discuss the most appropriate public health response under each scenario and emphasize how further data collection and analyses are required to more reliably evaluate the observed time trends and the relative importance of forces shaping the epidemic. Our study highlights how drug resistance markers can be used as epidemiologic sentinels to devise public health solutions.

Anti-HIV Agents↗
PubMed2005

Multidrug resistance among persons with tuberculosis in California, 1994-2003.

CONTEXT: Between 1994 and 2003, tuberculosis (TB) cases in California declined 33% (4834 to 3224). However, in 2003 California reported the largest number of cases in the nation, and over the past decade the proportion of cases with multidrug-resistant tuberculosis (MDR-TB) has not decreased. OBJECTIVE: To describe the magnitude, trends, geographic distribution, clinical characteristics, risk factors, and outcomes of MDR-TB cases reported to the California registry of Reports of Verified Cases of TB. DESIGN, SETTING, AND CASES: Analysis of 38,291 TB cases reported from all 61 local health jurisdictions in California during 1994-2003. Multidrug-resistant TB was defined as resistance to at least isoniazid and rifampin. MAIN OUTCOME MEASURES: Results of univariate and multivariable analyses of MDR-TB magnitude, trends, geographic distribution, clinical characteristics, associated factors, and outcomes. RESULTS: Of 38,291 reported TB cases, 28,712 (75%) were tested for resistance to at least isoniazid and rifampin; of these, 407 MDR-TB cases (1.4%) were reported from 38 of 61 California health jurisdictions (62%); the proportion of MDR-TB cases did not significantly change over the study period (P = .87). Cases of MDR-TB were twice as likely to have cavitary lesions compared with non-MDR-TB cases (P<.001) and were 7 times more likely to have reported previous treatment for TB (P<.001). Of MDR-TB cases with outcomes, 231 (67%) completed therapy, and those with MDR-TB were significantly less likely to complete therapy than those without MDR-TB (P<.001). Multivariate analysis identified previous TB diagnosis, positive acid-fast bacilli sputum smear results, Asian/Pacific Islander ethnicity, time in the United States less than 5 years at the time of diagnosis, and outcomes of "died" and "moved" as factors associated with MDR-TB. CONCLUSIONS: Multidrug-resistant TB, an airborne disease with limited, costly treatment options, persists in 1% to 2% of all cases despite California's control efforts. Local and global TB control efforts are needed to prevent the further development and spread of MDR-TB.

Adolescent↗
PubMed2005

Seasonal effects in the elimination of trachoma.

The World Health Organization currently recommends annual mass antibiotic treatment to eliminate the ocular chlamydia that cause blinding trachoma. Active trachoma is believed to be seasonal in many areas of the world, and the optimal season in which to treat has not as yet been established. Here we use mathematical models of disease transmission to demonstrate that ideally, treatment should be administered before the low season to have the greatest chance of locally eliminating infection.

Humans↗
PubMed2004

A decrease in drug resistance levels of the HIV epidemic can be bad news.

Transient decreases in the proportion of individuals newly infected with an HIV-resistant virus (primary resistance) are documented for several cities of North America, including San Francisco. Using a staged SI deterministic model, we identified three potential causes consistent with the history of the epidemic: (1) increase in risky behaviour, (2) reduction in the proportion of HIV-acutely infected individuals undergoing treatment, and (3) replacement of mono- and dual-drug therapies with triple-drug therapies. Although observed patterns resemble scenario 1 most closely, these explanations are not mutually exclusive and may have contributed synergistically to the decline. Under scenario 1 the counterintuitive situation arises where, although the proportion of primary resistance cases decreases transiently, the epidemic worsens because the actual numbers of infected individuals and of drug resistance carriers increases. Our results call for improved efforts to control the epidemic in developed nations, and highlight the usefulness of drug resistant strains as epidemiological markers.

Antiretroviral Therapy, Highly Active↗
PubMed2004

The effect of treatment on pathogen virulence.

The optimal virulence of a pathogen is determined by a trade-off between maximizing the rate of transmission and maximizing the duration of infectivity. Treatment measures such as curative therapy and case isolation exert selective pressure by reducing the duration of infectivity, reducing the value of duration-increasing strategies to the pathogen and favoring pathogen strategies that maximize the rate of transmission. We extend the trade-off models of previous authors, and represents the reproduction number of the pathogen as a function of the transmissibility, host contact rate, disease-induced mortality, recovery rate, and treatment rate, each of which may be influenced by the virulence. We find that when virulence is subject to a transmissibility-mortality trade-off, treatment can lead to an increase in optimal virulence, but that in other scenarios (such as the activity-recovery trade-off) treatment decreases the optimal virulence. Paradoxically, when levels of treatment rise with pathogen virulence, increasing control efforts may raise predicted levels of optimal virulence. Thus we show that conflict can arise between the epidemiological benefits of treatment and the evolutionary risks of heightened virulence.

Communicable Diseases↗
PubMed2004

Logistics of community smallpox control through contact tracing and ring vaccination: a stochastic network model.

BACKGROUND: Previous smallpox ring vaccination models based on contact tracing over a network suggest that ring vaccination would be effective, but have not explicitly included response logistics and limited numbers of vaccinators. METHODS: We developed a continuous-time stochastic simulation of smallpox transmission, including network structure, post-exposure vaccination, vaccination of contacts of contacts, limited response capacity, heterogeneity in symptoms and infectiousness, vaccination prior to the discontinuation of routine vaccination, more rapid diagnosis due to public awareness, surveillance of asymptomatic contacts, and isolation of cases. RESULTS: We found that even in cases of very rapidly spreading smallpox, ring vaccination (when coupled with surveillance) is sufficient in most cases to eliminate smallpox quickly, assuming that 95% of household contacts are traced, 80% of workplace or social contacts are traced, and no casual contacts are traced, and that in most cases the ability to trace 1-5 individuals per day per index case is sufficient. If smallpox is assumed to be transmitted very quickly to contacts, it may at times escape containment by ring vaccination, but could be controlled in these circumstances by mass vaccination. CONCLUSIONS: Small introductions of smallpox are likely to be easily contained by ring vaccination, provided contact tracing is feasible. Uncertainties in the nature of bioterrorist smallpox (infectiousness, vaccine efficacy) support continued planning for ring vaccination as well as mass vaccination. If initiated, ring vaccination should be conducted without delays in vaccination, should include contacts of contacts (whenever there is sufficient capacity) and should be accompanied by increased public awareness and surveillance.

Computer Simulation↗
PubMed2004

HIV-1 superinfection and viral diversity.

OBJECTIVE: Sequential acquisition of viral variants, or HIV-1 superinfection, has been proposed to explain the high fractions of recombinant viruses observed in some geographical regions, but only a few cases of superinfection in humans have been reported. Animal models suggest that susceptibility to superinfection may be restricted to a short period of time after initial infection, possibly due to maturation of broad antiviral immune responses. METHODS: A mathematical model involving a system of differential equations was developed to identify transmission and superinfection patterns that would lead to the observed global patterns of viral diversity. RESULTS: Requirements for a high prevalence of infections involving recombinant viruses include high viral infectivity, the presence of highly sexually active core groups, and introduction of divergent viruses early in the epidemic spread of HIV-1. Restricted superinfection could explain the persistent predominance of single virus subtypes in regions with well-established HIV-1 epidemics. The rate of recombination within individuals was not strongly related to recombinant fractions in populations. CONCLUSIONS: HIV-1 superinfection restricted to early HIV-1 infection could account for the high fraction of recombinant virus infections observed in populations. The relationship between recombination in cellular infections and recombinant fractions in populations is complex and depends on epidemiological factors and biological factors that can be modeled.

Computer Simulation↗
PubMed2004

Modeling the HIV protease inhibitor adherence-resistance curve by use of empirically derived estimates.

The standard view postulates a bell-shaped relationship between adherence to therapy and development of drug-resistant human immunodeficiency virus (HIV), with a resistance peak at a moderate level of adherence. This relationship has not been confirmed empirically. We statistically modeled the relationship between adherence and development of drug resistance, using empirically defined relationships of the rate of viral suppression and drug-resistance-mutation accumulation derived from patients receiving protease-inhibitor-based therapy. We found that the maximal rate of drug resistance occurs at 87% adherence and declines modestly at 100% adherence. Higher levels of viral suppression at 100% adherence (a marker of greater regimen potency) progressively reduce the overall population rate of drug resistance and shift the peak resistance rate to lower levels of adherence.

Adult↗
PubMed2004

Decline in HIV infectivity following the introduction of highly active antiretroviral therapy.

OBJECTIVE: Little is known about the degree to which widespread use of antiretroviral therapy in a community reduces uninfected individuals' risk of acquiring HIV. We estimated the degree to which the probability of HIV infection from an infected partner (the infectivity) declined following the introduction of highly active antiretroviral therapy (HAART) in San Francisco. DESIGN: Homosexual men from the San Francisco Young Men's Health Study, who were initially uninfected with HIV, were asked about sexual practices, and tested for HIV antibodies at each of four follow-up visits during a 6-year period spanning the advent of widespread use of HAART (1994-1999). METHODS: We estimated the infectivity of HIV (per-partnership probability of transmission from an infected partner) using a probabilistic risk model based on observed incident infections and self-reported sexual risk behavior, and tested the hypothesis that infectivity was the same before and after HAART was introduced. RESULTS: A total of 534 homosexual men were evaluated. Decreasing trends in HIV seroincidence were observed despite increases in reported number of unprotected receptive anal intercourse partners. Conservatively assuming a constant prevalence of HIV infection between 1994 and 1999, HIV infectivity decreased from 0.120 prior to widespread use of HAART, to 0.048 after the widespread use of HAART- a decline of 60% (P=0.028). CONCLUSIONS: Use of HAART by infected persons in a community appears to reduce their infectiousness and therefore may provide an important HIV prevention tool.

Adolescent↗
PubMed2003

Bias due to secondary transmission in estimation of attributable risk from intervention trials.

BACKGROUND: An important concept in epidemiology is attributable risk, defined as the difference in risk between an exposed and an unexposed group. For example, in an intervention trial, the attributable risk is the difference in risk between a group that receives an intervention and another that does not. A fundamental assumption in estimating the attributable risk associated with the intervention is that disease outcomes are independent. When estimating population risks associated with treatment regimens designed to affect exposure to infectious pathogens, however, there may be bias due to the fact that infectious pathogens can be transmitted from host to host causing a potential statistical dependency in disease status among participants. METHODS: To estimate this bias, we used a mathematical model of community- and household-level disease transmission to explicitly incorporate the dependency among participants. We illustrate the method using a plausible model of infectious diarrheal disease. RESULTS: Analysis of the model suggests that this bias in attributable risk estimates is a function of transmission from person to person, either directly or indirectly via the environment. CONCLUSIONS: By incorporating these dependencies among individuals in a transmission model, we show how the bias of attributable risk estimates could be quantified to adjust effect estimates reported from intervention trials.

Bias↗