How social structures, space, and behaviors shape the spread of infectious diseases using chikungunya as a case study.

Whether an individual becomes infected in an infectious disease outbreak depends on many interconnected risk factors, which may relate to characteristics of the individual (e.g., age, sex), his or her close relatives (e.g., household members), or the wider community. Studies monitoring individuals in households or schools have helped elucidate the determinants of transmission in small social structures due to advances in statistical modeling; but such an approach has so far largely failed to consider individuals in the wider context they live in. Here, we used an outbreak of chikungunya in a rural community in Bangladesh as a case study to obtain a more comprehensive characterization of risk factors in disease spread. We developed Bayesian data augmentation approaches to account for uncertainty in the source of infection, recall uncertainty, and unobserved infection dates. We found that the probability of chikungunya transmission was 12% [95% credible interval (CI): 8-17%] between household members but dropped to 0.3% for those living 50 m away (95% CI: 0.2-0.5%). Overall, the mean transmission distance was 95 m (95% CI: 77-113 m). Females were 1.5 times more likely to become infected than males (95% CI: 1.2-1.8), which was virtually identical to the relative risk of being at home estimated from an independent human movement study in the country. Reported daily use of antimosquito coils had no detectable impact on transmission. This study shows how the complex interplay between the characteristics of an individual and his or her close and wider environment contributes to the shaping of infectious disease epidemics.

Rates of hospital-acquired respiratory illness in Bangladeshi tertiary care hospitals: results from a low-cost pilot surveillance strategy.

BACKGROUND: Patients hospitalized in resource-poor health care settings are at increased risk for hospital-acquired respiratory infections due to inadequate infrastructure. METHODS: From 1 April 2007 through 31 March 2008, we used a low-cost surveillance strategy to identify new onset of respiratory symptoms in patients hospitalized for >72 h and in health care workers in medicine and pediatric wards at 3 public tertiary care hospitals in Bangladesh. RESULTS: During 46,273 patient-days of observation, we recorded 136 episodes of hospital-acquired respiratory disease, representing 1.7% of all patient hospital admissions; rates by ward ranged from 0.8 to 15.8 cases per 1000 patient-days at risk. We identified 22 clusters of respiratory disease, 3 of which included both patients and health care workers. Of 226 of heath care workers who worked on our surveillance wards, 61 (27%) experienced a respiratory illness during the study period. The cost of surveillance was US$43 per month per ward plus 30 min per day in data collection. CONCLUSIONS: Patients on these study wards frequently experienced hospital-acquired respiratory infections, including 1 in every 20 patients hospitalized for >72 h on 1 ward. The surveillance method was useful in calculating rates of hospital-acquired respiratory illness and could be used to enhance capacity to quickly detect outbreaks of respiratory disease in health care facilities where systems for outbreak detection are currently limited and to test interventions to reduce transmission of respiratory pathogens in resource-poor settings.

Incidence of and risk factors for hospital-acquired diarrhea in three tertiary care public hospitals in Bangladesh.

During April 2007-April 2010, surveillance physicians in adult and pediatric medicine wards of three tertiary public hospitals in Bangladesh identified patients who developed hospital-acquired diarrhea. We calculated incidence of hospital-acquired diarrhea. To identify risk factors, we compared these patients to randomly selected patients from the same wards who were admitted > 72 hours without having diarrhea. The incidence of hospital-acquired diarrhea was 4.8 cases per 1,000 patient-days. Children < 1 year of age were more likely to develop hospital-acquired diarrhea than older children. The risk of developing hospital-acquired diarrhea increased for each additional day of hospitalization beyond 72 hours, whereas exposure to antibiotics within 72 hours of admission decreased the risk. There were three deaths among case-patients; all were infants. Patients, particularly young children, are at risk for hospital-acquired diarrhea and associated deaths in Bangladeshi hospitals. Further research to identify the responsible organisms and transmission routes could inform prevention strategies.

Risk practices for animal and human anthrax in Bangladesh: an exploratory study.

INTRODUCTION: From August 2009 to October 2010, International Centre for Diarrheal Disease Research, Bangladesh and the Institute of Epidemiology, Disease Control and Research together investigated 14 outbreaks of anthrax which included 140 animal and 273 human cases in 14 anthrax-affected villages. Our investigation objectives were to explore the context in which these outbreaks occurred, including livestock rearing practices, human handling of sick and dead animals, and the anthrax vaccination program. METHODS: Field anthropologists used qualitative data-collection tools, including 15 hours of unstructured observations, 11 key informant interviews, 32 open-ended interviews, and 6 group discussions in 5 anthrax-affected villages. RESULTS: Each cattle owner in the affected communities raised a median of six ruminants on their household premises. The ruminants were often grazed in pastures and fed supplementary rice straw, green grass, water hyacinth, rice husk, wheat bran, and oil cake; lactating cows were given dicalcium phosphate. Cattle represented a major financial investment. Since Islamic law forbids eating animals that die from natural causes, when anthrax-infected cattle were moribund, farmers often slaughtered them on the household premises while they were still alive so that the meat could be eaten. Farmers ate the meat and sold it to neighbors. Skinners removed and sold the hides from discarded carcasses. Farmers discarded the carcasses and slaughtering waste into ditches, bodies of water, or open fields. Cattle in the affected communities did not receive routine anthrax vaccine due to low production, poor distribution, and limited staffing for vaccination. CONCLUSION: Slaughtering anthrax-infected animals and disposing of butchering waste and carcasses in environments where ruminants live and graze, combined with limited vaccination, provided a context that permitted repeated anthrax outbreaks in animals and humans. Because of strong financial incentives, slaughtering moribund animals and discarding carcasses and waste products will likely continue. Long-term vaccination coverage for at-risk animal populations may reduce anthrax infection.