Norovirus transmission dynamics: a modelling review.

Norovirus is one of the leading causes of viral gastroenteritis worldwide and responsible for substantial morbidity, mortality and healthcare costs. To further understanding of the epidemiology and control of norovirus, there has been much recent interest in describing the transmission dynamics of norovirus through mathematical models. In this study, we review the current modelling approaches for norovirus transmission. We examine the data and methods used to estimate these models that vary structurally and parametrically between different epidemiological contexts. Many of the existing studies at population level have focused on the same case notification dataset, whereas models from outbreak settings are highly specific and difficult to generalise. In this review, we explore the consistency in the description of norovirus transmission dynamics and the robustness of parameter estimates between studies. In particular, we find that there is considerable variability in estimates of key parameters such as the basic reproduction number, which may mean that the effort required to control norovirus at the population level may currently be underestimated.Takeda Pharmaceutical

Relationships Among HIV/AIDS Orphanhood, Stigma, and Symptoms of Anxiety and Depression in South African Youth: A Longitudinal Investigation Using a Path Analysis Framework

Cross-sectional research has demonstrated that HIV/AIDS orphanhood is associated with anxiety and depression and that HIV/AIDS-related stigma is a risk factor for these outcomes. This study used a longitudinal data set to determine whether relationships between HIV/AIDS orphanhood and anxiety/depression scores (measured at 4-year follow-up) operate indirectly via perceived stigma. Youths from poor communities around Cape Town were interviewed in 2005 (n = 1,025) and followed up in 2009 (n = 723). At baseline, HIV/AIDS-orphaned youth reported significantly higher stigma and depression scores than youth not orphaned by HIV/AIDS. At follow-up, HIV/AIDS-orphaned youth reported significantly higher stigma, anxiety, and depression scores. However, HIV/AIDS orphanhood was not directly associated with anxiety or depression. Instead, significant indirect effects (operating through perceived stigma) were obtained for both assessment periods. Results demonstrate that stigma persists across time and appears to mediate relationships between HIV/AIDS orphanhood and psychological distress. Interventions aiming to reduce stigma may help promote the mental health of HIV/AIDS-orphaned youth

Epidemiology and Cost of Nosocomial Gastroenteritis, Avon, England, 2002–2003

Implementing control measures rapidly may be effective in controlling gastroenteritis outbreaks

Patterns of self-reported behaviour change associated with receiving voluntary counselling and testing in a longitudinal study from Manicaland, Zimbabwe.

Voluntary counselling and testing (VCT) is promoted as a potential HIV prevention measure. We describe trends in uptake of VCT for HIV, and patterns of subsequent behaviour change associated with receiving VCT in a population-based open cohort in Manicaland, Zimbabwe. The relationship between receipt of VCT and subsequent reported behaviour was analysed using generalized linear models with random effects. At the third survey, 8.6% of participants (1,079/12,533), had previously received VCT. Women who received VCT, both those positive and negative, reduced their reported number of new partners. Among those testing positive, this risk reduction was enhanced with time since testing. Among men, no behavioural risk reduction associated with VCT was observed. Significant increases in consistent condom use, with regular or non-regular partners, following VCT, were not observed. This study suggests that, among women, particularly those who are infected, behavioural risk reduction does occur following VCT

Role of widows in the heterosexual transmission of HIV in Manicaland, Zimbabwe, 1998–2003

BACKGROUND: AIDS is the main driver of young widowhood in southern Africa. METHODS: The demographic characteristics of widows, their reported risk behaviours and the prevalence of HIV were examined by analysing a longitudinal population-based cohort of men and women aged 15-54 years in Manicaland, eastern Zimbabwe. The results from statistical analyses were used to construct a mathematical simulation model with the aim of estimating the contribution of widow behaviour to heterosexual HIV transmission. RESULTS: 413 (11.4%) sexually experienced women and 31 (1.2%) sexually experienced men were reported to be widowed at the time of follow-up. The prevalence of HIV was exceptionally high among both widows (61%) and widowers (male widows) (54%). Widows were more likely to have high rates of partner change and engage in a pattern of transactional sex than married women. Widowers took partners who were a median of 10 years younger than themselves. Mathematical model simulations of different scenarios of sexual behaviour of widows suggested that the sexual activity of widow(er)s may underlie 8-17% of new HIV infections over a 20-year period. CONCLUSIONS: This combined statistical analysis and model simulation suggest that widowhood plays an important role in the transmission of HIV in this rural Zimbabwean population. High-risk partnerships may be formed when widowed men and women reconnect to the sexual network

Verbal autopsy can consistently measure AIDS mortality: a validation study in Tanzania and Zimbabwe

BACKGROUND: Verbal autopsy is currently the only option for obtaining cause of death information in most populations with a widespread HIV/AIDS epidemic. METHODS: With the use of a data-driven algorithm, a set of criteria for classifying AIDS mortality was trained. Data from two longitudinal community studies in Tanzania and Zimbabwe were used, both of which have collected information on the HIV status of the population over a prolonged period and maintained a demographic surveillance system that collects information on cause of death through verbal autopsy. The algorithm was then tested in different times (two phases of the Zimbabwe study) and different places (Tanzania and Zimbabwe). RESULTS: The trained algorithm, including nine signs and symptoms, performed consistently based on sensitivity and specificity on verbal autopsy data for deaths in 15-44-year-olds from Zimbabwe phase I (sensitivity 79%; specificity 79%), phase II (sensitivity 83%; specificity 75%) and Tanzania (sensitivity 75%; specificity 74%) studies. The sensitivity dropped markedly for classifying deaths in 45-59-year-olds. CONCLUSIONS: Verbal autopsy can consistently measure AIDS mortality with a set of nine criteria. Surveillance should focus on deaths that occur in the 15-44-year age group for which the method performs reliably. Addition of a handful of questions related to opportunistic infections would enable other widely used verbal autopsy tools to apply this validated method in areas for which HIV testing and hospital records are unavailable or incomplete

Gastro-enteritis outbreak among Nordic patients with psoriasis in a health centre in Gran Canaria, Spain: a cohort study

BACKGROUND: Between November 2 and 10, 2002 several patients with psoriasis and personnel staying in the health centre in Gran Canaria, Spain fell ill with diarrhoea, vomiting or both. Patient original came from Norway, Sweden and Finland. The patient group was scheduled to stay until 8 November. A new group of patients were due to arrive from 7 November. METHODS: A retrospective cohort study was conducted to assess the extent of the outbreak, to identify the source and mode of transmission and to prevent similar problems in the following group. RESULTS: Altogether 41% (48/116) of persons staying at the centre fell ill. Norovirus infection was suspected based on clinical presentations and the fact that no bacteria were identified. Kaplan criteria were met. Five persons in this outbreak were hospitalised and the mean duration of diarrhoea was 3 days. The consequences of the illness were more severe compared to many other norovirus outbreaks, possibly because many of the cases suffered from chronic diseases and were treated with drugs reported to affect the immunity (methotrexate or steroids). During the two first days of the outbreak, the attack rate was higher in residents who had consumed dried fruit (adjusted RR = 3.1; 95% CI: 1.4–7.1) and strawberry jam (adjusted RR = 1.9; 95% CI: 0.9–4.1) than those who did not. In the following days, no association was found. The investigation suggests two modes of transmission: a common source for those who fell ill during the two first days of the outbreak and thereafter mainly person to person transmission. This is supported by a lower risk associated with the two food items at the end of the outbreak. CONCLUSIONS: We believe that the food items were contaminated by foodhandlers who reported sick before the outbreak started. Control measures were successfully implemented; food buffets were banned, strict hygiene measures were implemented and sick personnel stayed at home >48 hours after last symptoms

HIV decline in Zimbabwe due to reductions in risky sex? Evidence from a comprehensive epidemiological review

Background Recent data from antenatal clinic (ANC) surveillance and general population surveys suggest substantial declines in human immunodeficiency virus (HIV) prevalence in Zimbabwe. We assessed the contributions of rising mortality, falling HIV incidence and sexual behaviour change to the decline in HIV prevalence. Methods Comprehensive review and secondary analysis of national and local sources on trends in HIV prevalence, HIV incidence, mortality and sexual behaviour covering the period 1985-2007. Results HIV prevalence fell in Zimbabwe over the past decade (national estimates: from 29.3% in 1997 to 15.6% in 2007). National census and survey estimates, vital registration data from Harare and Bulawayo, and prospective local population survey data from eastern Zimbabwe showed substantial rises in mortality during the 1990s levelling off after 2000. Direct estimates of HIV incidence in male factory workers and women attending pre- and post-natal clinics, trends in HIV prevalence in 15-24-year-olds, and back-calculation estimates based on the vital registration data from Harare indicated that HIV incidence may have peaked in the early 1990s and fallen during the 1990s. Household survey data showed reductions in numbers reporting casual partners from the late 1990s and high condom use in non-regular partnerships between 1998 and 2007. Conclusions These findings provide the first convincing evidence of an HIV decline accelerated by changes in sexual behaviour in a southern African country. However, in 2007, one in every seven adults in Zimbabwe was still infected with a life-threatening virus and mortality rates remained at crisis leve

A cost effectiveness and capacity analysis for the introduction of universal rotavirus vaccination in Kenya : comparison between Rotarix and RotaTeq vaccines

Background Diarrhoea is an important cause of death in the developing world, and rotavirus is the single most important cause of diarrhoea associated mortality. Two vaccines (Rotarix and RotaTeq) are available to prevent rotavirus disease. This analysis was undertaken to aid the decision in Kenya as to which vaccine to choose when introducing rotavirus vaccination. Methods Cost-effectiveness modelling, using national and sentinel surveillance data, and an impact assessment on the cold chain. Results The median estimated incidence of rotavirus disease in Kenya was 3015 outpatient visits, 279 hospitalisations and 65 deaths per 100,000 children under five years of age per year. Cumulated over the first five years of life vaccination was predicted to prevent 34% of the outpatient visits, 31% of the hospitalizations and 42% of the deaths. The estimated prevented costs accumulated over five years totalled US$1,782,761 (direct and indirect costs) with an associated 48,585 DALYs. From a societal perspective Rotarix had a cost-effectiveness ratio of US$142 per DALY (US$5 for the full course of two doses) and RotaTeq US$288 per DALY ($10.5 for the full course of three doses). RotaTeq will have a bigger impact on the cold chain compared to Rotarix. Conclusion Vaccination against rotavirus disease is cost-effective for Kenya irrespective of the vaccine. Of the two vaccines Rotarix was the preferred choice due to a better cost-effectiveness ratio, the presence of a vaccine vial monitor, the requirement of fewer doses and less storage space, and proven thermo-stability