No abstract

The capsular serotype is a major determinant of both pneumococcal duration of carriage and attack rate. Published invasive odds ratios are a reliable and practical method of determining capsular serotype invasiveness and will be valuable for investigating and characterizing emerging capsular serotypes in the context of conjugate vaccination.

Nasal carriage of Staphylococcus aureus is a major risk factor for invasive S. aureus disease. The aim of this study was to define factors associated with carriage. We conducted a prospective, longitudinal communitybased study of infants and their mothers for a period of 6 months following delivery. The epidemiology of carriage was examined for 100 infant-mother pairs. Infant carriage varied significantly with age, falling from 40 to 50% during the first 8 weeks to 21% by 6 months. Determinants of infant S. aureus carriage included maternal carriage, breastfeeding, and number of siblings. Bacterial typing of S. aureus was performed by pulsed-field gel electrophoresis and multilocus sequence typing. The majority of individuals carried a single strain of S. aureus over time, and the mother was the usual source for colonizing isolates in infants. The effect of other components of the normal nasal flora on the development of S. aureus carriage was examined in 157 consecutive infants. Negative associations (putative bacterial interference) between S. aureus and other species occurred early in infancy but were not sustained. An increasing antistaphylococcal effect observed over time was not attributable to bacterial interference. S. aureus carriage in infants is likely to be determined by a combination of host, environmental, and bacterial factors, but bacterial interference does not appear to be an ultimate determinant of carrier status.Staphylococcus aureus is a major cause of community-acquired and nosocomial sepsis (7, 23). The rising prevalence of antibiotic-resistant strains, such as methicillin-resistant S. aureus and S. aureus with reduced susceptibility to glycopeptides (15,17,22), increases the need to prevent disease through the identification and modification of risk factors. Three sets of observations indicate that nasal carriage of S. aureus is an important risk factor for sepsis with this organism: carriers have higher rates of infection than noncarriers (16,29,30,31); the strain causing infection is usually the carriage strain in a given individual (16,18,28,31); and eradication of carriage reduces nosocomial infection (2,10,20,31). Temporary eradication of S. aureus in those at high risk of sepsis is desirable but relies on the unlikely premise of sustained susceptibility to antibiotics such as mupirocin. There is a need to develop alternative methods of S. aureus eradication, the success of which may depend on a detailed understanding of the determinants of carriage. The relative importance of host, bacterial, and environmental factors in determining S. aureus carriage is currently unknown. The aim of this study was to explore these factors during a prospective, longitudinal community-based study of carriage in mothers and their infants for a period of 6 months after delivery. MATERIALS AND METHODSStudy design. The study was conducted in two parts. Epidemiological factors influencing infant carriage were examined for a group of 100 consecutively recruited infants and their mothers who were derived fr...

Neisseria lactamica, a harmless human commensal found predominantly in the upper respiratory tracts of infants, is closely related to Neisseria meningitidis, a pathogen of global significance. Colonization with N. lactamica may be responsible for the increase in immunity to meningococcal disease that occurs during childhood, when rates of meningococcal carriage are low. This observation has led to the suggestion that N. lactamica whole cells or components are potential constituents of novel meningococcal vaccines. However, the dynamics of carriage and population diversity of N. lactamica in children are poorly understood, presenting difficulties for the choice of representative isolates for use in vaccine development. This problem was addressed by the multilocus sequence typing of N. lactamica isolates from two longitudinal studies of bacterial carriage in infants. The studies comprised 100 and 216 subjects, with N. lactamica carriage monitored from age 4 weeks until age 96 weeks and from age 2 weeks until age 24 weeks, respectively. The maximum observed carriage rate was 44% at 56 weeks of age, with isolates obtained on multiple visits for the majority (54 of 75, 72%) of carriers. The N. lactamica isolates were genetically diverse, with 69 distinct genotypes recovered from the 75 infants. Carriage was generally long-lived, with an average rate of loss of under 1% per week during the 28 weeks following acquisition. Only 11 of the 75 infants carried more than one genotypically unique isolate during the course of the study. Some participants shared identical isolates with siblings, but none shared identical isolates with their parents. These findings have implications for the design of vaccines based on this organism.