Estimated Transmission Rate Research Articles

Improving throughput in WiMAX communication at vehicular speeds

WiMAX technology has emerged as an exciting technology for next generation broadband wireless network with promises to offer high throughput and long coverage. WiMAX, however, has yet to prove its merits when the wireless nodes are not fixed and move at high vehicular speeds. Recent studies suggest that WiMAX offers limited throughput when a mobile node travels at vehicular speeds. Multipath fading causes high bit error rates at the receiver and is considered the main reason behind low throughput at high vehicular speeds. Bit error rates and maximum packet size govern the packet error rates, and error recovery for higher number of corrupted packets is not an attractive option for many real-time applications with tight delay and jitter constraints. In this paper, we present a mathematical model for estimating bit error rates in WiMAX communication at vehicular speeds. The estimated bit error probability is taken into account for proactively computing an optimum packet size that offers the best chance of achieving improved throughput. We further propose a model that can be used to increase the utility of real-time wireless applications e.g., video surveillance systems in public train based on the knowledge of estimated transmission rates. We simulated the proposed and other standard schemes for a centralized video surveillance system in a public train where the train moves at high speeds and sends real-time video data to a central control room through wireless channels. The results show that the proposed scheme achieves significantly higher throughput, lower jitter and higher utility gain compared to the standard schemes.

Homologous whole bacterin vaccination is not able to reduce Streptococcus suis serotype 9 strain 7997 transmission among pigs or colonization

Streptococcus suis (S. suis) is an important porcine pathogen worldwide, and antibiotics are often applied to treat or prevent clinical signs. Vaccination could be an alternative measure to reduce the abundant use of antimicrobials. The aim of this study was to determine the effect of vaccination with homologues whole bacterin vaccine containing S. suis serotype 9 strain 7997 on transmission of this serotype among pigs and on mucosal colonization. Caesarean derived, colostrum deprived pigs (N=50) were housed pair wise. Thirteen pairs were vaccinated intramuscularly with 2-3×10(9) colony forming units (CFU) inactivated S. suis serotype 9 per dose and α-tocopherolactetaat as adjuvant at 3 and 5 weeks of age; twelve pairs served as non-vaccinated controls. At 7 weeks of age, one pig of each pair was intranasally inoculated with 1-2×10(9)CFU of the homologues strain, whereas the other pig of each pair was contact-exposed. Tonsil brushings and saliva swabs were collected for 4 weeks, and tested for the presence of S. suis by bacteriological culture. No differences in number of S. suis in the tonsils or saliva samples or in clinical signs were observed between vaccinated and control pigs. In all pairs, transmission between inoculated and contact exposed pigs occurred, and no difference was observed in rate at which this occurred. The estimated transmission rate parameter β between vaccinated pigs was β(v)=5.27/day, and for non-vaccinated pigs β(nv)=2.77/day (P=0.18). It was concluded that vaccination against S. suis serotype 9 did not reduce transmission, nor colonization and that there were no indications that protection against clinical signs was induced.

Estimating Duration of Infection with Avidity Assays: Potential Limitations and Recommendations for Improvement

Recent infections often have higher pathogen loads. The number of recent infections can therefore be used to estimate transmission rates in a host population. Antibody avidity assays are an emerging technique to infer infection age in both domestic and wild animals. These assays have the potential to supplant intensive mark-recapture efforts for identification of recent infections, but their results may be confounded by antibody titer. We examined the effectiveness of an avidity assay for identifying recent infections of Sin Nombre virus, a hantavirus in North America that establishes a chronic infection in deer mice (Peromyscus maniculatus). We found that assay performance statistics such as sensitivity, specificity, and positive predictive value for low avidity scores were significantly improved when we accounted for antibody titer in the analyses. Without accounting for titer, avidity assays may classify samples with low titers as recent infections regardless of actual infection history, thereby overestimating the number of recent infections in a population and inflating estimates of transmission rates and/or human exposure risk. We recommend that antibody titers meet a minimum threshold for use in avidity assays, and we emphasize the importance of considering titer and dilution in the validation of newly developed avidity assays.

S12.1 Transmission of human papillomavirus infections

BackgroundThere have been few studies of the sexual transmission of human papillomavirus (HPV) between partners. Our objective was to estimate transmission rates among persons with documented sexual exposure to an...

Inferring Epidemiological Parameters on the Basis of Allele Frequencies

In this article, I develop a methodology for inferring the transmission rate and reproductive value of an epidemic on the basis of genotype data from a sample of infected hosts. The epidemic is modeled by a birth-death process describing the transmission dynamics in combination with an infinite-allele model describing the evolution of alleles. I provide a recursive formulation for the probability of the allele frequencies in a sample of hosts and a Bayesian framework for estimating transmission rates and reproductive values on the basis of observed allele frequencies. Using the Bayesian method, I reanalyze tuberculosis data from the United States. I estimate a net transmission rate of 0.19/year [0.13, 0.24] and a reproductive value of 1.02 [1.01, 1.04]. I demonstrate that the allele frequency probability under the birth-death model does not follow the well-known Ewens' sampling formula that holds under Kingman's coalescent.

Rhabdoviruses in Two Species of Drosophila: Vertical Transmission and a Recent Sweep

Insects are host to a diverse range of vertically transmitted micro-organisms, but while their bacterial symbionts are well-studied, little is known about their vertically transmitted viruses. We have found that two sigma viruses (Rhabdoviridae) recently discovered in Drosophila affinis and Drosophila obscura are both vertically transmitted. As is the case for the sigma virus of Drosophila melanogaster, we find that both males and females can transmit these viruses to their offspring. Males transmit lower viral titers through sperm than females transmit through eggs, and a lower proportion of their offspring become infected. In natural populations of D. obscura in the United Kingdom, we found that 39% of flies were infected and that the viral population shows clear evidence of a recent expansion, with extremely low genetic diversity and a large excess of rare polymorphisms. Using sequence data we estimate that the virus has swept across the United Kingdom within the past ∼11 years, during which time the viral population size doubled approximately every 9 months. Using simulations based on our lab estimates of transmission rates, we show that the biparental mode of transmission allows the virus to invade and rapidly spread through populations at rates consistent with those measured in the field. Therefore, as predicted by our simulations, the virus has undergone an extremely rapid and recent increase in population size. In light of this and earlier studies of a related virus in D. melanogaster, we conclude that vertically transmitted rhabdoviruses may be common in insects and that these host–parasite interactions can be highly dynamic.

Using Approximate Bayesian Computation to Estimate Transmission Rates of Nosocomial Pathogens

In this paper, we apply a simulation based approach for estimating transmission rates of nosocomial pathogens. In particular, the objective is to infer the transmission rate between colonised health-care practitioners and uncolonised patients (and vice versa) solely from routinely collected incidence data. The method, using approximate Bayesian computation, is substantially less computer intensive and easier to implement than likelihood-based approaches we refer to here. We find through replacing the likelihood with a comparison of an efficient summary statistic between observed and simulated data that little is lost in the precision of estimated transmission rates. Furthermore, we investigate the impact of incorporating uncertainty in previously fixed parameters on the precision of the estimated transmission rates.

Model structure analysis to estimate basic immunological processes and maternal risk for parvovirus B19

After a steep monotone rise with age, the seroprevalence profiles for human parvovirus B19 (PVB19) display a decrease or plateau between the ages of 20 and 40, in each of 5 European countries. We investigate whether this phenomenon is induced by waning antibodies for PVB19 and, if this is the case, whether secondary infections are plausible, or whether boosting may occur. Several immunological scenarios are tested for PVB19 by fitting different compartmental dynamic transmission models to serological data using data on social contact patterns. The social contact approach has already been shown informative to estimate transmission rates and the basic reproduction number for infections transmitted predominantly through nonsexual social contacts. Our results show that for 4 countries, model selection criteria favor the scenarios allowing for waning immunity at an age-specific rate over the assumption of lifelong immunity, assuming that the transmission rates are directly proportional to the contact rates. Different views on the evolution of the immune response to PVB19 infection lead to altered estimates of the age-specific force of infection and the basic reproduction number. The scenarios which allow for multiple infections during one lifetime predict a higher frequency of PVB19 infection in pregnant women and of associated fetal deaths. When prevaccination serological data are available, the framework developed in this paper could prove worthwhile to investigate these different scenarios for other infections as well, such as cytomegalovirus.

Potential for North American Mosquitoes (Diptera: Culicidae) to Transmit Rift Valley Fever Virus

To determine which arthropods should be targeted for control should Rift Valley fever virus (RVFV) be detected in North America, we evaluated Culex erraticus (Dyar and Knab), Culex erythrothorax Dyar, Culex nigripalpus Theobald, Culex pipiens L., Culex quinquefasciatus Say, Culex tarsalis Coquillett, Aedes dorsalis (Wiedemann), Aedes vexans (Meigen), Anopheles quadrimaculatus Say, and Culicoides sonorensis Wirth and Jones from the western, midwestern, and southern United States for their ability to transmit RVFV. Female mosquitoes were allowed to feed on adult hamsters inoculated with RVFV, after which engorged mosquitoes were incubated for 7-21 d at 260C, then allowed to refeed on susceptible hamsters, and tested to determine infection, dissemination, and transmission rates. Other specimens were inoculated intrathoracically, held for 7 d, and then allowed to feed on a susceptible hamster to check for a salivary gland barrier. When exposed to hamsters with viremias > or =10(8.8) plaque-forming units/ml blood, Cx. tarsalis transmitted RVFV efficiently (infection rate = 93%, dissemination rate = 56%, and estimated transmission rate = 52%). In contrast, when exposed to the same virus dose, none of the other species tested transmitted RVFV efficiently. Estimated transmission rates for Cx. erythrothorax, Cx. pipiens, Cx. erraticus, and Ae. dorsalis were 10, 8, 4, and 2%, respectively, and for the remaining species were < or = 1%. With the exception of Cx. tarsalis and Cx. pipiens, all species tested had moderate to major salivary gland barriers. None of the C. sonorensis became infected and none of the An. quadrimaculatus tested transmitted RVFV by bite, even after intrathoracic inoculation, indicating that these species would not be competent vectors of RVFV. Although Ae. vexans from Florida and Louisiana were relatively efficient vectors of RVFV, specimens of this species captured in Colorado or California were virtually incompetent, illustrating the need to evaluate local population for their ability to transmit a pathogen. In addition to laboratory vector competence, factors such as seasonal density, host feeding preference, longevity, and foraging behavior should be considered when determining the potential role that these species could play in RVFV transmission.

Within-flock transmission of H7N1 highly pathogenic avian influenza virus in turkeys during the Italian epidemic in 1999–2000

Highly pathogenic avian influenza (HPAI) viruses show different disease dynamics between virus strains and host species, and therefore epidemic field data are very valuable. This study used field data of the HPAI H7N1 epidemic which affected Northern Italy in 1999–2000. Field mortality data was back-calculated into a S-I-format to estimate the transmission rate parameter β, indicating the number of birds infected per infectious bird per time unit. The bird-infectious period was assumed to be 2 days, and all birds were assumed to die after this infectious period. The estimated β for HPAI H7N1 virus transmission in turkeys was 1.43 (95% CI: 1.17–1.74). Farm risk factors such as flock size and age of the turkeys did not influence the estimated transmission rate parameter.

Per-contact probability of HIV transmission in homosexual men in Sydney in the era of HAART

The objective of this study is to estimate per-contact probability of HIV transmission in homosexual men due to unprotected anal intercourse (UAI) in the era of HAART. Data were collected from a longitudinal cohort study of community-based HIV-negative homosexual men in Sydney, Australia. A total of 1427 participants were recruited from June 2001 to December 2004. They were followed up with 6-monthly detailed behavioral interviews and annual testing for HIV till June 2007. Data were used in a bootstrapping method, coupled with a statistical analysis that optimized a likelihood function for estimating the per-exposure risks of HIV transmission due to various forms of UAI. During the study, 53 HIV seroconversion cases were identified. The estimated per-contact probability of HIV transmission for receptive UAI was 1.43% [95% confidence interval (CI) 0.48-2.85] if ejaculation occurred inside the rectum, and it was 0.65% (95% CI 0.15-1.53) if withdrawal prior to ejaculation was involved. The estimated transmission rate for insertive UAI in participants who were circumcised was 0.11% (95% CI 0.02-0.24), and it was 0.62% (95% CI 0.07-1.68) in uncircumcised men. Thus, receptive UAI with ejaculation was found to be approximately twice as risky as receptive UAI with withdrawal or insertive UAI for uncircumcised men and over 10 times as risky as insertive UAI for circumcised men. Despite the fact that a high proportion of HIV-infected men are on antiretroviral treatment and have undetectable viral load, the per-contact probability of HIV transmission due to UAI is similar to estimates reported from developed country settings in the pre-HAART era.

Assessing the role of undetected colonization and isolation precautions in reducing Methicillin-Resistant Staphylococcus aureustransmission in intensive care units

BackgroundScreening and isolation are central components of hospital methicillin-resistant Staphylococcus aureus (MRSA) control policies. Their prevention of patient-to-patient spread depends on minimizing undetected and unisolated MRSA-positive patient days. Estimating these MRSA-positive patient days and the reduction in transmission due to isolation presents a major methodological challenge, but is essential for assessing both the value of existing control policies and the potential benefit of new rapid MRSA detection technologies. Recent methodological developments have made it possible to estimate these quantities using routine surveillance data.MethodsColonization data from admission and weekly nares cultures were collected from eight single-bed adult intensive care units (ICUs) over 17 months. Detected MRSA-positive patients were isolated using single rooms and barrier precautions. Data were analyzed using stochastic transmission models and model fitting was performed within a Bayesian framework using a Markov chain Monte Carlo algorithm, imputing unobserved MRSA carriage events.ResultsModels estimated the mean percent of colonized-patient-days attributed to undetected carriers as 14.1% (95% CI (11.7, 16.5)) averaged across ICUs. The percent of colonized-patient-days attributed to patients awaiting results averaged 7.8% (6.2, 9.2). Overall, the ratio of estimated transmission rates from unisolated MRSA-positive patients and those under barrier precautions was 1.34 (0.45, 3.97), but varied widely across ICUs.ConclusionsScreening consistently detected >80% of colonized-patient-days. Estimates of the effectiveness of barrier precautions showed considerable uncertainty, but in all units except burns/general surgery and one cardiac surgery ICU, the best estimates were consistent with reductions in transmission associated with barrier precautions.

An evaluation of transmission routes for low pathogenicity avian influenza virus among chickens sold in live bird markets

Many theories about the modes of avian influenza virus (AIV) transmission have been proposed, but few have been quantified, and none within a flock or live bird market (LBM) setting where birds are often kept in stacked cages. We describe a novel experimental design and the results collected for the purpose of estimating transmission rates specific to the potential modes of AIV transmission within an LBM. Chickens of the strains and ages found in California LBMs were inoculated with low pathogenicity AIV H6N2. Aerosol exposure was found to be the most important route of transmission for this H6N2 AIV. The handling of infectious chickens resulted in the transmission of H6N2 AIV, though the virus was not detectible by rRT-PCR. Chickens with fecal exposure to infected birds (median=8.0 DPI) had detectable virus earlier than in those with aerosol exposure only (median=10.0 DPI). Changes in the hemagglutinin sequence were not found to be associated with oropharyngeal or cloacal shedding in this study.

Transmission dynamics and economics of rabies control in dogs and humans in an African city

Human rabies in developing countries can be prevented through interventions directed at dogs. Potential cost-savings for the public health sector of interventions aimed at animal-host reservoirs should be assessed. Available deterministic models of rabies transmission between dogs were extended to include dog-to-human rabies transmission. Model parameters were fitted to routine weekly rabid-dog and exposed-human cases reported in N'Djaména, the capital of Chad. The estimated transmission rates between dogs (beta(d)) were 0.0807 km2/(dogs x week) and between dogs and humans (beta(dh)) 0.0002 km2/(dogs x week). The effective reproductive ratio (R(e)) at the onset of our observations was estimated at 1.01, indicating low-level endemic stability of rabies transmission. Human rabies incidence depended critically on dog-related transmission parameters. We simulated the effects of mass dog vaccination and the culling of a percentage of the dog population on human rabies incidence. A single parenteral dog rabies-mass vaccination campaign achieving a coverage of least 70% appears to be sufficient to interrupt transmission of rabies to humans for at least 6 years. The cost-effectiveness of mass dog vaccination was compared to postexposure prophylaxis (PEP), which is the current practice in Chad. PEP does not reduce future human exposure. Its cost-effectiveness is estimated at US $46 per disability adjusted life-years averted. Cost-effectiveness for PEP, together with a dog-vaccination campaign, breaks even with cost-effectiveness of PEP alone after almost 5 years. Beyond a time-frame of 7 years, it appears to be more cost-effective to combine parenteral dog-vaccination campaigns with human PEP compared to human PEP alone.

Updated Annual HIV Transmission Rates in the United States, 1977-2006

Updated Annual HIV Transmission Rates in the United States, 1977-2006

Effect of H7N1 vaccination on highly pathogenic avian influenza H7N7 virus transmission in turkeys

This study describes the results of a transmission experiment with highly pathogenic avian influenza (HPAI) H7N7 virus in 12-week-old turkeys. Cloacal and tracheal swabs as well as serum samples were taken to monitor the infection both in inoculated and in susceptible contact turkeys, which were all either unvaccinated, vaccinated once or vaccinated twice with H7N1. Swabs were tested by real-time RT-PCR and serum samples with hemagglutination inhibition test (HI). Unvaccinated contact birds had a mean infectious period of 6.2 days, and an estimated transmission rate parameter of 1.26 per infectious bird per day. However, no virus shedding was found in inoculated vaccinated turkeys and thus we concluded that vaccination with H7N1 protected against challenge with HPAI H7N7 virus.

Use of cluster-graphs from spoligotyping data to study genotype similarities and a comparison of three indices to quantify recent tuberculosis transmission among culture positive cases in French Guiana during a eight year period

BackgroundFrench Guiana has the highest tuberculosis (TB) burden among all French departments, with a strong increase in the TB incidence over the last few years. It is now uncertain how best to explain this incidence. The objective of this study was to compare three different methods evaluating the extent of recent TB transmission in French Guiana.MethodsWe conducted a population-based molecular epidemiology study of tuberculosis in French Guiana based on culture-positive TB strains (1996 to 2003, n = 344) to define molecular relatedness between isolates, i.e. potential transmission events. Phylogenetic relationships were inferred by comparing two methods: a "cluster-graph" method based on spoligotyping results, and a minimum spanning tree method based on both spoligotyping and variable number of tandem DNA repeats (VNTR). Furthermore, three indices attempting to reflect the extent of recent TB transmission (RTIn, RTIn-1 and TMI) were compared.ResultsMolecular analyses showed a total amount of 120 different spoligotyping patterns and 273 clinical isolates (79.4%) that were grouped in 49 clusters. The comparison of spoligotypes from French Guiana with an international spoligotype database (SpolDB4) showed that the majority of isolates belonged to major clades of M. tuberculosis (Haarlem, 22.6%; Latin American-Mediterranean, 23.3%; and T, 32.6%). Indices designed to quantify transmission of tuberculosis gave the following values: RTIn = 0.794, RTIn-1 = 0.651, and TMI = 0.146.ConclusionOur data showed a high number of Mycobacterium tuberculosis clusters, suggesting a high level of recent TB transmission, nonetheless an estimation of transmission rate taking into account cluster size and mutation rate of genetic markers showed a low ongoing transmission rate (14.6%). Our results indicate an endemic mode of TB transmission in French Guiana, with both resurgence of old spatially restricted genotypes, and a significant importation of new TB genotypes by migration of TB infected persons from neighgouring high-incidence countries.

Vector Competence of Selected African Mosquito (Diptera: Culicidae) Species for Rift Valley Fever Virus

Outbreaks of Rift Valley fever (RVF) in Egypt, Yemen, and Saudi Arabia have indicated the potential for this disease to spread from its enzootic areas in sub-Saharan Africa. Because little is known about the potential for most African mosquito species to transmit RVF virus (family Bunyaviridae, genus Phlebovirus, RVFV), we conducted studies to determine the vector competence of selected African species of mosquitoes for this virus. All eight species tested [Aedes palpalis (Newstead), Aedes mcintoshi Huang, Aedes circumluteolus (Theobald), Aedes calceatus Edwards, Aedes aegypti (L.), Culex antennatus (Becker), Culex pipiens (L.), and Culex quinquefasciatus Say], were susceptible to infection, and all except Ae. calceatus, Ae. aegypti and Cx. quinquefasciatus transmitted RVFV by bite after oral exposure. Estimated transmission rates for mosquitoes that successfully transmitted RVFV by bite ranged from 5% for Ae. mcintoshi to 39% for Ae. palpalis for mosquitoes that fed on a hamster with a viremia > or = 10(8) plaque-forming units of virus/ml. We did not recover RVFV from any of 3,138 progeny of infected female mosquitoes. RVFV is unusual among arboviruses in that it has been isolated in nature from a large number of species and that numerous mosquitoes and other arthropods are able to transmit this virus in the laboratory. The recent introduction and spread of West Nile virus into the Americas and the spread of RVFV to the Arabian Peninsula illustrates the potential for viruses, once enzootic in Africa, to spread to other parts of the world.

Multivariate Markov Process Models for the Transmission of Methicillin‐ResistantStaphylococcus Aureusin a Hospital Ward

Methicillin-resistant Staphylococcus Aureus (MRSA) is a pathogen that continues to be of major concern in hospitals. We develop models and computational schemes based on observed weekly incidence data to estimate MRSA transmission parameters. We extend the deterministic model of McBryde, Pettitt, and McElwain (2007, Journal of Theoretical Biology 245, 470-481) involving an underlying population of MRSA colonized patients and health-care workers that describes, among other processes, transmission between uncolonized patients and colonized health-care workers and vice versa. We develop new bivariate and trivariate Markov models to include incidence so that estimated transmission rates can be based directly on new colonizations rather than indirectly on prevalence. Imperfect sensitivity of pathogen detection is modeled using a hidden Markov process. The advantages of our approach include (i) a discrete valued assumption for the number of colonized health-care workers, (ii) two transmission parameters can be incorporated into the likelihood, (iii) the likelihood depends on the number of new cases to improve precision of inference, (iv) individual patient records are not required, and (v) the possibility of imperfect detection of colonization is incorporated. We compare our approach with that used by McBryde et al. (2007) based on an approximation that eliminates the health-care workers from the model, uses Markov chain Monte Carlo and individual patient data. We apply these models to MRSA colonization data collected in a small intensive care unit at the Princess Alexandra Hospital, Brisbane, Australia.

Transmission disequilibrium analysis of the functional 5-HT3A receptor variant C178T in early-onset obsessive—compulsive disorder

The 5-HT(3) receptor is unique among the serotonin receptors in that it is a ligand-gated ion channel. Dysfunction of the serotonin system is thought to contribute to the pathogenesis of obsessive-compulsive disorder (OCD). Apart from the standard treatment with serotonin reuptake inhibitors and behavioural therapy, a 5-HT(3) receptor antagonist has recently been shown to benefit some OCD patients, suggesting the 5-HT(3) receptor as a serotonergic candidate gene in the polygenic aetiology of OCD. A functional regulatory variant of the 5-HT(3A) receptor influences 5-HT(3) receptor expression, serotonin metabolites in cerebrospinal fluid, and amygdala reactivity. We therefore assessed whether this C178T variant influences the risk of developing OCD. In a family-based approach employing the transmission disequilibrium test, we analysed a unique sample of 75 children and adolescents with OCD, as well as their biological parents. We found no evidence for a preferential transmission of either allele to the patients--the estimated transmission rate for the C allele was 0.51 (95% CI 0.36-0.65). This argues against an involvement of the 5-HT(3A) receptor in the polygenic aetiology of early-onset OCD.