BackgroundMathematical modelling of infectious diseases transmitted by the respiratory or close-contact route (e.g., pandemic influenza) is increasingly being used to determine the impact of possible interventions. Although mixing patterns are known to be crucial determinants for model outcome, researchers often rely on a priori contact assumptions with little or no empirical basis. We conducted a population-based prospective survey of mixing patterns in eight European countries using a common paper-diary methodology.Methods and Findings7,290 participants recorded characteristics of 97,904 contacts with different individuals during one day, including age, sex, location, duration, frequency, and occurrence of physical contact. We found that mixing patterns and contact characteristics were remarkably similar across different European countries. Contact patterns were highly assortative with age: schoolchildren and young adults in particular tended to mix with people of the same age. Contacts lasting at least one hour or occurring on a daily basis mostly involved physical contact, while short duration and infrequent contacts tended to be nonphysical. Contacts at home, school, or leisure were more likely to be physical than contacts at the workplace or while travelling. Preliminary modelling indicates that 5- to 19-year-olds are expected to suffer the highest incidence during the initial epidemic phase of an emerging infection transmitted through social contacts measured here when the population is completely susceptible.ConclusionsTo our knowledge, our study provides the first large-scale quantitative approach to contact patterns relevant for infections transmitted by the respiratory or close-contact route, and the results should lead to improved parameterisation of mathematical models used to design control strategies.
Streptococcus pneumoniae (pneumococcus) is a major cause of worldwide mortality and morbidity, and to a large extent is vaccine-preventable. Nasopharyngeal carriage of pneumococcus precedes disease and is the source of pneumococcal spread between people. The use of vaccine effect on carriage as part of the vaccine licensure and post-vaccine introduction evaluation could facilitate and expand the licensure of new, life-saving pneumococcal vaccines and enable a comprehensive estimate of population effects after vaccine introduction. The authors provide a review of the evidence supporting pneumococcal carriage at the individual level as an immediate and necessary precursor to pneumococcal disease. Based on such a causal link between carriage and disease, the authors emphasize the role of information on pneumococcal carriage in vaccine trials and in public health decision-making.
Streptococcus pneumoniae (the pneumococcus) causes diseases from otitis media to life-threatening invasive infection. The species is extremely antigenically and clonally diverse. We wished to determine odds ratios (ORs) for serotypes and clones of S. pneumoniae that cause invasive disease in Finland. A total of 224 isolates of S. pneumoniae from cases of invasive disease in children <2 years of age in Finland between 1995 and 1999 were serotyped, and sequence types (STs) were determined by multilocus sequence typing. These STs were compared with a previously published carriage data set. STs from invasive disease were significantly less diverse than those from carriage (invasive disease, 0.038 ؎ 0.01; carriage, 0.019 ؎ 0.005). The ORs of serotypes 14, 18C, 19A, and 6B were significantly greater than 1, indicating association with invasive disease. The ORs of 6A and 11A were significantly less than 1. The difference between 6A and 6B is significant, which suggests that relatively subtle changes in the capsule may have a dramatic effect upon disease potential. We found that ST 156, the Spain 9V -3 clone which mainly expressed serotype 14 in Finland, is strongly associated with invasive disease (OR, 10.1; 95% confidence interval, 1.3 to 79.5). Significant associations with invasive disease were also detected for STs 482, 191, 124, and 138, and associations with carriage were detected for STs 485 and 62. These results demonstrate the invasive phenotype of the serotype 14 variant of the Spain 9V -3 clone and differences between members of the same serogroup in invasive disease potential.
The state of pneumococcal carriage—that is, pneumococcal colonization in the nasopharynx of healthy persons—represents a reservoir for the spread of pneumococci among individuals. In light of the introduction of new pneumococcal conjugate vaccines, further knowledge on the dynamics of pneumococcal carriage is important. Different serotypes (strains) of pneumococcus are known to compete with each other in colonizing human hosts. Understanding the strength and mode of between-serotype competition is important because of its implications for vaccine-induced changes in the ecology of pneumococcal carriage. Competition may work through reduced acquisition of new serotypes, due to concurrent carriage in the individual, or through enhanced clearance of serotypes in carriers who harbor more than 1 serotype simultaneously. The authors employed longitudinal data (1999–2001) on pneumococcal carriage in Danish day-care children to analyze between-serotype competition. The data included observations of carriage in children who had not been vaccinated against pneumococcus, and the level of pneumococcal antibiotic resistance and antibiotic usage in the community was very low. Clearance of any single serotype was not affected by simultaneous carriage of other serotypes. In contrast, acquisition of other serotypes in already-colonized hosts was weak (relative rate of acquisition = 0.09, 95% credible interval: 0.05, 0.15).
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