Characteristics of human encounters and social mixing patterns relevant to infectious diseases spread by close contact: a survey in Southwest Uganda.

BACKGROUND: Quantification of human interactions relevant to infectious disease transmission through social contact is central to predict disease dynamics, yet data from low-resource settings remain scarce. METHODS: We undertook a social contact survey in rural Uganda, whereby participants were asked to recall details about the frequency, type, and socio-demographic characteristics of any conversational encounter that lasted for ≥5 min (henceforth defined as 'contacts') during the previous day. An estimate of the number of 'casual contacts' (i.e. < 5 min) was also obtained. RESULTS: In total, 566 individuals were included in the study. On average participants reported having routine contact with 7.2 individuals (range 1-25). Children aged 5-14 years had the highest frequency of contacts and the elderly (≥65 years) the fewest (P < 0.001). A strong age-assortative pattern was seen, particularly outside the household and increasingly so for contacts occurring further away from home. Adults aged 25-64 years tended to travel more often and further than others, and males travelled more frequently than females. CONCLUSION: Our study provides detailed information on contact patterns and their spatial characteristics in an African setting. It therefore fills an important knowledge gap that will help more accurately predict transmission dynamics and the impact of control strategies in such areas.

The epidemiology of gonorrhoea in London: a Bayesian spatial modelling approach.

Data obtained from genitourinary medicine clinics through a comprehensive surveillance system were used in a Bayesian mixed-effects Poisson regression model to explore socio-demographic individual and ecological risk factors for gonorrhoea in London, as well as its spatial clustering. The spatial analysis was performed at the Middle-layer Super Output Area level (median population size 7200). A total of 12452 individuals were diagnosed during the 2-year study period (2009-2010). The study confirmed the presence of 'core areas' of high incidence, and identified 'core' high-risk groups, in particular young adults (16-29 years), males, black Caribbeans and more deprived areas. The individual (age, sex, ethnicity) and area-level (deprivation, teenage pregnancies, students) model covariates accounted for 48% of the variance. Most of the remaining variance was explained by the spatial effect, thus capturing other spatially distributed factors associated with gonorrhoea, such as local sexual networks. These findings will be useful in identifying areas for targeted interventions, such as STI testing and health promotion.

Epidemiology of tuberculosis in children in London, 2009-2011: are opportunities for prevention being missed?

SETTING: London, United Kingdom. OBJECTIVE: To explore missed opportunities (MO) for the prevention of tuberculosis (TB) in children aged 0-15 years. DESIGN: Parents/guardians of children aged <15 years diagnosed with TB and reported through surveillance were interviewed about bacille Calmette-Guérin vaccination (MO-V) or contact tracing and screening for TB (MO-C) via an algorithm reflecting eligibility. RESULTS: Annual TB incidence was 12 per 100,000 (65/100,000 in Black Africans, 20/100,000 in Indian or Pakistani children). The response rate was 36% (145/405). About 20% of UK-born children had not been vaccinated. MO-V was not associated with any particular factor. Contact with a known TB case before illness had occurred in 71 children (49%; 71% in those aged 0-1 years vs. 30% in those aged 11-15 years), of whom 64 (91%) were diagnosed through contact tracing. MO-C had been conducted in six (4% overall). Children with MO-C were all of Black ethnic origin. Their index cases were family members (within their household) or relatives or family friends from abroad (outside their household). MO-C was not associated with any other factor. CONCLUSION: Although overall few missed opportunities for prevention had occurred, we recommend increased rigour when performing contact tracing in any case where a child may have been exposed.

The case-cohort design in outbreak investigations.

The use of the case-cohort design for outbreak investigations has been limited. Here we discuss its strengths and limitations based on real and fictitious examples. The case-cohort is a case­control study where controls are sampled from the initial population at risk, and may thus include both cases and non-cases. An advantage of the design, compared to traditional case-control studies, is that risk ratios can easily be obtained directly from the cross-product of exposed and unexposed cases and controls (rare disease assumption is not required). We illustrate this in the context of point source gastrointestinal outbreaks and in field studies on vaccine effectiveness. The design is also useful to investigate multiple outcomes with a unique sample of controls or to test hypotheses when different case-definitions (from the most sensitive to the most specific) are used for a particular outcome. Strengths and limitations are presented, and discussed in the context of outbreak investigations.