PubMed Health⌕ Search

Biomedical subjects

Babak Pourbohloul

Publications and source records attributed to Babak Pourbohloul.

10 recordsLinked to original sources
PubMed2006

A comparative analysis of influenza vaccination programs.

BACKGROUND: The threat of avian influenza and the 2004-2005 influenza vaccine supply shortage in the United States have sparked a debate about optimal vaccination strategies to reduce the burden of morbidity and mortality caused by the influenza virus. METHODS AND FINDINGS: We present a comparative analysis of two classes of suggested vaccination strategies: mortality-based strategies that target high-risk populations and morbidity-based strategies that target high-prevalence populations. Applying the methods of contact network epidemiology to a model of disease transmission in a large urban population, we assume that vaccine supplies are limited and then evaluate the efficacy of these strategies across a wide range of viral transmission rates and for two different age-specific mortality distributions. We find that the optimal strategy depends critically on the viral transmission level (reproductive rate) of the virus: morbidity-based strategies outperform mortality-based strategies for moderately transmissible strains, while the reverse is true for highly transmissible strains. These results hold for a range of mortality rates reported for prior influenza epidemics and pandemics. Furthermore, we show that vaccination delays and multiple introductions of disease into the community have a more detrimental impact on morbidity-based strategies than mortality-based strategies. CONCLUSIONS: If public health officials have reasonable estimates of the viral transmission rate and the frequency of new introductions into the community prior to an outbreak, then these methods can guide the design of optimal vaccination priorities. When such information is unreliable or not available, as is often the case, this study recommends mortality-based vaccination priorities.

Adolescent↗
PubMed2006

Coordinated response to SARS, Vancouver, Canada.

Two Canadian urban areas received travelers with severe acute respiratory syndrome (SARS) before the World Health Organization issued its alert. By July 2003, Vancouver had identified 5 cases (4 imported); Toronto reported 247 cases (3 imported) and 43 deaths. Baseline preparedness for pandemic threats may account for the absence of sustained transmission and fewer cases of SARS in Vancouver.

Adult↗
PubMed2005

Predicting epidemics on directed contact networks.

Contact network epidemiology is an approach to modeling the spread of infectious diseases that explicitly considers patterns of person-to-person contacts within a community. Contacts can be asymmetric, with a person more likely to infect one of their contacts than to become infected by that contact. This is true for some sexually transmitted diseases that are more easily caught by women than men during heterosexual encounters; and for severe infectious diseases that cause an average person to seek medical attention and thereby potentially infect health care workers (HCWs) who would not, in turn, have an opportunity to infect that average person. Here we use methods from percolation theory to develop a mathematical framework for predicting disease transmission through semi-directed contact networks in which some contacts are undirected-the probability of transmission is symmetric between individuals-and others are directed-transmission is possible only in one direction. We find that the probability of an epidemic and the expected fraction of a population infected during an epidemic can be different in semi-directed networks, in contrast to the routine assumption that these two quantities are equal. We furthermore demonstrate that these methods more accurately predict the vulnerability of HCWs and the efficacy of various hospital-based containment strategies during outbreaks of severe respiratory diseases.

Communicable Disease Control↗
PubMed2005

The unexpected impact of a Chlamydia trachomatis infection control program on susceptibility to reinfection.

BACKGROUND: After the introduction of a program to control Chlamydia trachomatis infection in British Columbia, Canada, case rates fell from 216 cases/100,000 population in 1991 to 104 cases/100,000 population in 1997. Since 1998, rates have increased, and case counts now exceed those recorded before the intervention. METHODS: We used Cox proportional-hazards survival analysis and developed a compartmental mathematical model to investigate the cause of resurgence in chlamydia cases. RESULTS: Cox proportional-hazards survival analysis showed that the relative risk of C. trachomatis reinfection has increased 4.6% per year since 1989, with the increased risk greatest among the young and greater among women than men. A compartmental mathematical model of C. trachomatis transmission showed that a control strategy based on shortening the average duration of infection results in an early reduction in prevalence followed by a rebound in prevalence, reproducing the observed trends. CONCLUSIONS: We speculate that a C. trachomatis infection control program based on early case identification and treatment interferes with the effects of immunity on population susceptibility to infection and that, in the absence of strategies to alter sexual networks, a vaccine will be needed to halt the spread of infection at the population level.

Adolescent↗
PubMed2005

Effect of immune response on transmission dynamics for sexually transmitted infections.

Transmission dynamics for sexually transmitted infections (STIs) exhibit a large degree of heterogeneity, much of which has been attributed to behavioral variability. However, because STI transmission concentrates among individuals who frequently change sex partners, immune responses also are likely to contribute to the heterogeneity in STI transmission dynamics. We review both theoretical and experimental data on the effects of immunity on STI transmission dynamics. We conclude that research should be directed more intensively toward the characterization of sexual network structures, together with qualitative and quantitative analyses of the immune responses of individuals who are identifiable within the network structure itself. Elucidation of the immunobiological and behavioral factors that shape STI transmission should inform better STI prevention and control programs.

Contact Tracing↗
PubMed2005

Network theory and SARS: predicting outbreak diversity.

Many infectious diseases spread through populations via the networks formed by physical contacts among individuals. The patterns of these contacts tend to be highly heterogeneous. Traditional "compartmental" modeling in epidemiology, however, assumes that population groups are fully mixed, that is, every individual has an equal chance of spreading the disease to every other. Applications of compartmental models to Severe Acute Respiratory Syndrome (SARS) resulted in estimates of the fundamental quantity called the basic reproductive number R0--the number of new cases of SARS resulting from a single initial case--above one, implying that, without public health intervention, most outbreaks should spark large-scale epidemics. Here we compare these predictions to the early epidemiology of SARS. We apply the methods of contact network epidemiology to illustrate that for a single value of R0, any two outbreaks, even in the same setting, may have very different epidemiological outcomes. We offer quantitative insight into the heterogeneity of SARS outbreaks worldwide, and illustrate the utility of this approach for assessing public health strategies.

Adult↗
PubMed2005

Modeling control strategies of respiratory pathogens.

Effectively controlling infectious diseases requires quantitative comparisons of quarantine, infection control precautions, case identification and isolation, and immunization interventions. We used contact network epidemiology to predict the effect of various control policies for a mildly contagious disease, such as severe acute respiratory syndrome, and a moderately contagious disease, such as smallpox. The success of an intervention depends on the transmissibility of the disease and the contact pattern between persons within a community. The model predicts that use of face masks and general vaccination will only moderately affect the spread of mildly contagious diseases. In contrast, quarantine and ring vaccination can prevent the spread of a wide spectrum of diseases. Contact network epidemiology can provide valuable quantitative input to public health decisionmaking, even before a pathogen is well characterized.

British Columbia↗
PubMed2003

Targeted mass treatment for syphilis with oral azithromycin.

From mid 1997 to end of 1999, there was a sexually-transmitted infectious syphilis outbreak mainly in heterosexual people in British Columbia, Canada, that was concentrated in Vancouver. The rate across the province increased from less than 0.5 to 3.4 per 100000, and the rate in Vancouver reached 12.9 per 100000. We aimed to eliminate the syphillis outbreak by treating people at risk of infection. In 2000, a targeted mass treatment programme provided azithromycin (1.8 g orally) to 4384 at-risk residents in this city. After the programme, syphilis frequency fell significantly for 6 months (p=0.016), but rose again in 2001. Results from curve fitting analyses showed that the number of cases in 2001 (177) was higher than expected (0.0001<p<0.0044). This rate rebound and the absence of a sustained effect suggest that targeted mass treatment for syphilis, even though feasible, should not be done routinely.

Adolescent↗
PubMed2003

Impact of mass treatment on syphilis transmission: a mathematical modeling approach.

BACKGROUND: Since 1997 Vancouver (British Columbia, Canada) has experienced an outbreak of heterosexually transmitted infectious syphilis, which prompted a mass treatment campaign in early 2000 in an attempt to control the disease. By 1 year postintervention, syphilis cases had rebounded significantly. We investigate the cause of this postintervention rebound. GOAL: We argue that the observed rebound postintervention may have been the result of the natural dynamics of disease transmission in an open population, in response to the partial application of mass treatment in the sexually active subgroup. STUDY DESIGN: We used a mathematical model that describes the transmission dynamics of syphilis in a population. RESULTS: The observed postintervention rebound is related to the mass treatment intervention. CONCLUSION: Our results suggest that mass treatment may not be an optimal strategy to control the transmission of syphilis if complete coverage of high-frequency transmitters cannot be achieved and if population mobility is relatively high.

Adolescent↗