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Biomedical subjects

A C Ghani

Publications and source records attributed to A C Ghani.

29 records · Page 2Linked to original sources
PubMed1998

Epidemiological determinants of the pattern and magnitude of the vCJD epidemic in Great Britain.

Understanding the epidemiology and aetiology of new-variant Creutzfeldt-Jakob (vCJD) disease in humans has become increasingly important given the scientific evidence linking it to bovine spongiform encephalopathy (BSE) in cattle and hence the wide exposure of the population of Great Britain (GB) to potentially infectious tissue. The recent analysis undertaken to determine the risk to the population from dorsal route ganglia illustrated the danger in presenting point estimates rather than ranges of scenarios in the face of uncertainty. We present a mathematical template that relates the past pattern of the BSE epidemic in cattle to the future course of any vCJD epidemic in humans, and use extensive scenario analysis to explore the wide range of possible outcomes given the uncertainty in epidemiological determinants. We demonstrate that the average number of humans infected by one infectious bovine and the incubation period distribution are the two epidemiological factors that have the greatest impact on epidemic size and duration. Using the time-series of the BSE epidemic and the cases seen to date, we show that the minimum length of the incubation period is approximately nine years, and that at least 20% of the cases diagnosed to date were exposed prior to 1986. We also demonstrate that the current age distribution of vCJD cases can only arise if younger people were either exposed to a greater extent, more susceptible to infection, or have shorter incubation periods. Extensive scenario analyses show that given the information currently available, the very high degree of uncertainty in the future size of the epidemic will remain for the next 3-5 years. Furthermore, we demonstrate that this uncertainty is unlikely to be reduced by mass screening for late-stage infection.

Creutzfeldt-Jakob Syndrome↗
PubMed1998

Sampling biases and missing data in explorations of sexual partner networks for the spread of sexually transmitted diseases.

The structures of sexual partner networks are important in determining patterns of transmission of STDs including HIV. Empirical data on sexual partnerships and sexual partner networks collected through sampling individuals are a non-random sample of partnerships and network structures even if individuals are sampled randomly. This has the potential to bias estimates of measures describing the sexual partner network. In addition, biases may be introduced through non-response and missing data. Using Monte Carlo simulation, we investigate the biases that are introduced in estimates measures of the sexual partner network through three common sampling methods. The results indicate that substantial systematic biases are introduced. The direction and magnitude of these biases suggest that, by ignoring them, the risk for the establishment and persistence of infection in a population may be underestimated.

Bias↗
PubMed1998

BSE in Northern Ireland: epidemiological patterns past, present and future.

By 30 January 1998, there had been 170,259 confirmed cases of BSE in Great Britain (GB), 1766 confirmed cases in Northern Ireland (NI) (2 January 1998), and 276 confirmed cases in the Republic of Ireland (31 January 1998). Analysis of the epidemiological patterns in the NI epidemic reveals significant clustering of cases in herds and counties. The observed clustering of cases within herds results in lower per capita incidence of BSE in previously unaffected herds, providing support for the introduction of a certified herd scheme in NI. By fitting a backcalculation model to the case data, we can estimate the number of animals infected with the aetiological agent of BSE and project the number of future cases. We predict that the epidemic will decline rapidly, with approximately 99 cases (95% confidence interval 30,504) occurring in the five year period 1997-2001.

Animals↗
PubMed1998

Partner notification for gonorrhoea: a comparative study with a provincial and a metropolitan UK clinic.

OBJECTIVE: To compare partner notification practice and outcomes at a provincial and a metropolitan clinic. DESIGN: Prospective study, following standardisation of partner notification policy. SETTINGS: Sheffield Department of Genitourinary Medicine, Royal Hallamshire Hospital and Jefferiss Wing Centre for Sexual Health, St Mary's Hospital, London. SUBJECTS: Consecutive patients with culture positive gonorrhoea between October 1994 and March 1996 who were interviewed by a health adviser. RESULTS: In Sheffield, 235 cases reported 659 outstanding contacts, of whom 129 (20%) were subsequently screened, and 65 (50%) had gonorrhoea. At St Mary's 510 cases reported 2176 outstanding contacts, of whom 98 (5%) were known to have been screened, and 53 (54%) had gonorrhoea. Patient or provider referral agreements appeared more productive in Sheffield, where 60% resulted in contact attendance, compared with 13% at St Mary's. Provider referral was used more frequently in Sheffield, for 44% of referrals, compared with 1% at St Mary's. Multivariate analysis showed that partner notification was less effective for casual and short term (< 7 days) partnerships in both centres, and for homosexual men at St Mary's. CONCLUSION: Partner notification outcomes were better in the provincial setting where contact attendance could be recorded more reliably and provider referral was used more extensively. The high proportion of contacts who remained untraced in both settings indicates the need for complementary screening and prevention initiatives.

Adult↗
PubMed1997

Analysis of dam-calf pairs of BSE cases: confirmation of a maternal risk enhancement.

We investigate whether a calf born to a dam that develops bovine spongiform encephalopathy (BSE) (prior or subsequent to the birth) is itself at an enhanced risk of developing BSE. Analyses utilize the main database on reported BSE cases in the British cattle herd maintained by the Central Veterinary Laboratory in Weybridge to trace the dams of BSE-affected animals born following the ruminant feed ban in July 1988. The data reveal a significantly enhanced risk of disease in calves born to BSE-affected dams, with the risk being greatest when birth occurs after the onset of clinical signs of disease in the dam. The dependence of the maternally enhanced risk on the maternal incubation stage at birth argues for a significant component of direct maternal transmission of the aetiological agent of BSE, and offers little support for the hypothesis of genetic predisposition. Using a statistical likelihood model, we obtain estimates of the rate of direct maternal transmission by maternal incubation stage; however, biases in the available data make these values minimum estimates.

Animals↗
PubMed1997

The epidemiology of BSE in cattle herds in Great Britain. I. Epidemiological processes, demography of cattle and approaches to control by culling.

This paper explores the key epidemiological processes and demographic factors that determined the pattern of transmission of the aetiological agent of bovine spongiform encephalopathy (BSE) in cattle herds in Great Britain (GB). The analyses presented utilize data from published and unpublished experimental studies and from the GB central database of confirmed BSE cases. We review the experimental and epidemiological evidence that has both confirmed indirect horizontal transmission via the consumption of infectious material as the major transmission route and provided information on the duration and variability of the dose-dependent incubation period of BSE in cattle. The epidemiological and genetic data pertaining to the possible existence of maternal transmission and/or genetically variable susceptibility to infection is discussed. The demography of British cattle is characterized and the impacts of key demographic features on the observed epidemic profile are discussed. In the main BSE case database, analyses reveal that BSE cases cluster significantly at both the holding and county scale. Furthermore, analysis of longitudinal patterns reveal substantial temporal within-holding correlation. Such clustering of cases suggests a highly heterogeneous infection process. The paper ends with a discussion of how analyses of spatio-temporal clustering inform the design of targeted culling programmes aimed at reducing future disease incidence. We show how the retrospective implementation of culling policies on the BSE case database allows the qualitative evaluation of policy performance, but that model predictions of future trends in case incidence are required to estimate the precise impact of any current or future programme.

Age Factors↗
PubMed1997

The role of sexual partnership networks in the epidemiology of gonorrhea.

BACKGROUND: Empirical studies have the potential to collect data on patterns of sexual mixing and network structures. GOAL: To explore the contribution of different network measures in sexually transmitted disease epidemiology. STUDY DESIGN: Individual-based stochastic simulations of a network of sexual partnerships and sexually transmitted disease transmission are analyzed using logistic regression. RESULTS AND CONCLUSIONS: Measures accumulated over times similar to the duration of infection are more informative than are static cross sections. The patterns of sexual mixing and network structure influence patterns of infection. In particular, the establishment of infection is most sensitive to the proportion of nonmonogamous pairs, the component distribution and cohesion among those with high activity. The subsequent prevalence is most sensitive to the assortativeness of mixing in the high-activity class and a measure of cohesion, both of which reflect the decrease in prevalence brought about by less widespread connections. A person's risk for infection is determined by local rather than global network structures.

Contact Tracing↗
PubMed1995

Hospital costs of treating haemophilic patients infected with HIV.

OBJECTIVE: To calculate the costs of treating HIV-infected haemophilic patients. DESIGN: Two-year retrospective study of hospital-based resource use and costs, from April 1991 to March 1993. SETTING: Haemophilia Centre and Haemostasis Unit, Royal Free Hospital and School of Medicine, London, UK. PATIENTS: Sixty patients infected with HIV between October 1979 and July 1985. RESULTS: During the 2-year period a total of 1668 hospital visits were made by patients. The mean number of episodes per patient-year (PY) was 0.6 inpatient admissions, 11.5 outpatient visits and 1.8 day cases. The mean cost per PY was 32,528 pounds, with the majority of this spent on clotting factor concentrate products and haemophilia inpatient admissions (81%). A mean cost for HIV-related treatment of 6050 pounds was estimated. The additional cost incurred in switching this group of haemophilic patients from intermediate-purity factor concentrate to high-purity products was 8614 pounds per PY. When clotting factor concentrate and expenditure on haemophilia-related inpatient admissions were excluded, the mean cost of treating HIV infection per PY was 6065 pounds, varying with CD4+ count (< or = 50 x 10(6)/l, 13,093 pounds; 51-200 x 10(6)/l, 6521 pounds; 201-500 x 10(6)/l, 2848 pounds; > 501 x 10(6)/l, 1497 pounds). CONCLUSIONS: CD4+ count may be used as a marker of costs of HIV infection. The HIV-related cost estimates can be used for the planning of current and future hospital-based care in the National Health Service in the United Kingdom. The switch from intermediate-purity factor concentrate to high-purity products has increased the mean HIV-related cost per PY of treating haemophilic patients infected with HIV.

Acquired Immunodeficiency Syndrome↗
PubMedDate not supplied

Sexual partner networks in the transmission of sexually transmitted diseases. An analysis of gonorrhea cases in Sheffield, UK.

BACKGROUND AND OBJECTIVES: Routine contact tracing data on patients with gonorrhea are used to identify sexual partner networks. These are combined with gonococcal typing data to study patterns of transmission. The role of persons in transmission is discussed. STUDY DESIGN: Contact tracing data on patients with gonorrhea attending the Royal Hallamshire Hospital in Sheffield in 1988 and 1989 are analyzed. Gonococcal strains identified by auxotype/serovar (A/S) class are combined with these data to identify transmission paths. RESULTS: The network contained 1,272 persons, 724 (77%) of whom had gonorrhea during the study period. Four hundred two clusters of linked cases were identified. The largest cluster, containing 35 persons connected over 16 months, is discussed in greater detail to illustrate how these data may help identify patterns of transmission and the role of persons. CONCLUSION: Contact tracing data can be used to identify sexual partner networks and to study transmission patterns. Microbiologic data can aid interpretation. An person's risk of acquiring infection depends on indirect links as well as direct links. To understand patterns of transmission it may be important to distinguish between those involved in transmission and those only acquiring infection. Networks established through gonococcal transmission are also relevant to the transmission of other sexually transmitted diseases.

Adolescent↗