Showing papers by "Derrick W. Crook published in 2003"

Clonal Relationships between Invasive and Carriage Streptococcus pneumoniae and Serotype- and Clone-Specific Differences in Invasive Disease Potential

Abstract: By use of multilocus sequence typing, Streptococcus pneumoniae isolates causing invasive disease (n=150) were compared with those from nasopharyngeal carriage (n=351) among children in Oxford. The prevalence of individual clones (sequence types) and serotypes among isolates from invasive disease was related to their prevalence in carriage, and an odds ratio (OR) for invasive disease was calculated for the major clones and serotypes. All major carried clones and serotypes caused invasive disease, although their ability to do so varied greatly. Thus, 2 serotype 14 clones were approximately 10-fold overrepresented among disease isolates, compared with carriage isolates, whereas a serotype 3 clone was approximately 10-fold underrepresented. The lack of heterogeneity between the ORs of different clones of the same serotype, and analysis of isolates of the same genotype, but different serotype, suggested that capsular serotype may be more important than genotype in the ability of pneumococci to cause invasive disease.

Multilocus Sequence Typing System for Group B Streptococcus

Abstract: A multilocus sequence typing (MLST) system was developed for group B streptococcus (GBS). The system was used to characterize a collection (n = 152) of globally and ecologically diverse human strains of GBS that included representatives of capsular serotypes Ia, Ib, II, III, V, VI, and VIII. Fragments (459 to 519 bp) of seven housekeeping genes were amplified by PCR for each strain and sequenced. The combination of alleles at the seven loci provided an allelic profile or sequence type (ST) for each strain. A subset of the strains were characterized by restriction digest patterning, and these results were highly congruent with those obtained with MLST. There were 29 STs, but 66% of isolates were assigned to four major STs. ST-1 and ST-19 were significantly associated with asymptomatic carriage, whereas ST-23 included both carried and invasive strains. All 44 isolates of ST-17 were serotype III clones, and this ST appeared to define a homogeneous clone that was strongly associated with neonatal invasive infections. The finding that isolates with different capsular serotypes had the same ST suggests that recombination occurs at the capsular locus. A web site for GBS MLST was set up and can be accessed at http://sagalactiae.mlst.net. The GBS MLST system offers investigators a valuable typing tool that will promote further investigation of the population biology of this organism.

Determinants of Acquisition and Carriage of Staphylococcus aureus in Infancy

Abstract: 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 community-based 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.

Stability of Serotypes during Nasopharyngeal Carriage of Streptococcus pneumoniae

Abstract: Serotype changes among natural isolates of Streptococcus pneumoniae are well documented and occur by recombinational exchanges at the capsular biosynthetic locus. However, the frequency with which this phenomenon occurs within the nasopharynx of children is not clear and is likely to be highest in the nasopharynx of children, who have high rates of pneumococcal carriage. A birth cohort of 100 infants was studied, and pneumococci were recovered from nasopharyngeal samples taken at monthly intervals during the first 6 months of life and then at 2-monthly intervals until the age of 2 years. Among the 1,353 nasopharyngeal samples were 523 that contained presumptive pneumococci, and three colonies from each were serotyped. A total of 333 isolates, including all isolates of differing serotypes from the same child, were characterized by multilocus sequence typing. Sixty-eight children carried multiple serotypes during the first 2 years of life. Two children carried a typeable and a nonserotypeable pneumococcus of identical genotype, and five children carried genetically indistinguishable isolates of serotypes 15B and 15C. These isolates were considered, respectively, to be due to loss of capsule expression and the known ability of serotype 15B and 15C pneumococci to interconvert by loss or gain of an acetyl group on the capsular polysaccharide. In all other cases, isolates from the same children that differed in serotype also differed in genotype, indicating the acquisition of a different pneumococcal strain rather than a change in capsular type. There was therefore no evidence in this study for any change of serotype due to recombinational replacements at the capsular locus among the pneumococci carried within the nasopharynges of the children.

Near patient testing for influenza in children in primary care: comparison with laboratory test.

Abstract: Influenza is an important cause of acute respiratory illness in young children. Common complications include febrile convulsions, otitis media, bronchiolitis, and croup. In epidemic years attack rates among preschool children often exceed 40%. During these years children with influenza may account for up to 30% of the increase in antibiotic prescribing.1 Symptoms and signs of influenza in children are not specific and can mimic a range of other common respiratory viral pathogens. One quick way of reaching a precise diagnosis in primary care is to use a near patient test. Near patient testing for many conditions has expanded widely in primary care, though many tests have not been rigorously evaluated.2 Previous studies in children have compared near patient influenza tests with viral culture analysis using throat or nasal swabs.3 However, a nasopharyngeal aspirate is the best specimen for detecting influenza viruses, and …

Invasive pneumococcal disease in Oxford, 1985–2001: a retrospective case series

Abstract: AIMS: To describe a series of children with invasive pneumococcal disease (IPD). METHODS: A review of patient records for children aged 0-18 years admitted to the John Radcliffe Hospital with IPD from 1985 to 2001. Social deprivation was measured by the Jarman index. The proportion of children with congenital abnormalities was compared with national data. RESULTS: We identified 140 children with IPD; complete data were available for 136 children. The median age at diagnosis was 1.5 years. The social deprivation score of households of children with IPD was higher than that of the average Oxfordshire household (-2.5 v -7.3, p < 0.001). Forty four per cent of cases had at least one preceding health problem. The children with preceding health problems were significantly older than those with no preceding problems (median age 2.67 years, interquartile range 1.21 to 6.20 versus 1.11 years, interquartile range 0.51 to 2.21; p < 0.001). There was an increased risk of IPD for children with central nervous system malformations (OR = 99, 95% CI 31 to 236), congenital heart disease (OR = 62, 95% CI 24 to 131), and chromosomal abnormalities (OR = 32, 95% CI 6.6 to 96). CONCLUSIONS: There is an increased risk of IPD associated with increased social deprivation; and also with central nervous system malformations, congenital heart disease, and chromosomal abnormalities.