Retrospectively ECG-gated multi-detector row CT of the chest: does ECG-gating improve three-dimensional visualization of the bronchial tree?

PURPOSE

To determine the impact of retrospectively ECG-gated multi-detector row CT (MDCT) on three-dimensional (3D) visualization of the bronchial tree and virtual bronchoscopy (VB) as compared to non-ECG-gated data acquisition.

MATERIALS AND METHODS

Contrast-enhanced retrospectively ECG-gated and non-ECG-gated MDCT of the chest was performed in 25 consecutive patients referred for assessment of coronary artery bypass grafts and pathology of the ascending aorta. ECG-gated MDCT data were reconstructed in diastole using an absolute reverse delay of - 400 msec in all patients. In 10 patients additional reconstructions at - 200 msec, - 300 msec, and - 500 msec prior to the R-wave were performed. Shaded surface display (SSD) and virtual bronchoscopy (VB) for visualization of the bronchial segments was performed with ECG-gated and non-ECG-gated MDCT data. The visualization of the bronchial tree underwent blinded scoring. Effective radiation dose and signal-to-noise ratio (SNR) for both techniques were compared.

RESULTS

There was no significant difference in visualizing single bronchial segments using ECG-gated compared to non-ECG-gated MDCT data. However, the total sum of scores for all bronchial segments visualized with non-ECG-gated MDCT was significantly higher compared to ECG-gated MDCT (P < 0.05). The summary scores for visualization of bronchial segments for different diastolic reconstructions did not differ significantly. The effective radiation dose and the SNR were significantly higher with the ECG-gated acquisition technique (P < 0.05).

CONCLUSION

The bronchial tree is significantly better visualized when using non-ECG-gated MDCT compared to ECG-gated MDCT. Additionally, non-ECG-gated techniques require less radiation exposure. Thus, the current retrospective ECG-gating technique does not provide any additional benefit for 3D visualization of the bronchial tree and VB.

Hyperinvasive neonatal group B streptococcus has arisen from a bovine ancestor

The genetic relatedness and evolutionary relationships between group B streptococcus (GBS) isolates from humans and those from bovines were investigated by phylogenetic analysis of multilocus sequence typing data. The collection of isolates consisted of 111 GBS isolates from cows with mastitis and a diverse global collection of GBS isolates from patients with invasive disease (n = 83) and carriers (n = 69). Cluster analysis showed that the majority of the bovine isolates (93%) grouped into one phylogenetic cluster. The human isolates showed greater diversity and clustered separately from the bovine population. However, the homogeneous human sequence type 17 (ST-17) complex, known to be significantly associated with invasive neonatal disease, was the only human lineage found to be clustered within the bovine population and was distinct from all the other human lineages. Split decomposition analysis revealed that the human isolate ST-17 complex, the major hyperinvasive neonatal clone, has recently arisen from a bovine lineage.

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

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.

Clonal relationships between invasive and carriage Streptococcus pneumoniae and serotype- and clone-specific differences in invasive disease potential

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.

Stability of serotypes during nasopharyngeal carriage of Streptococcus pneumoniae

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.

MBL genotype and risk of invasive pneumococcal disease: a case-control study

BACKGROUND

Streptococcus pneumoniae is a major cause of morbidity and mortality in developed and developing countries. No common genetic determinants of susceptibility have been defined. Mannose-binding lectin (MBL) is a key mediator of innate host immunity that activates the complement pathway and directly opsonises some infectious pathogens. Mutations in three codons in the MBL gene have been identified, and individuals homozygous for a mutant genotype have very little or no serum MBL. We did a case-control study in the UK to assess whether these mutant genotypes were associated with invasive pneumococcal disease.

METHODS

The frequencies of genotypes defined by the three mutations in codons 52, 54, and 57, and a functional promoter polymorphism at -221, were compared in a two-stage study of 337 patients with invasive pneumococcal disease and 1032 controls. All individuals were recruited from an ethnically homogeneous white population in Oxfordshire, UK. Patients had S pneumoniae isolated from a normally sterile site.

FINDINGS

In our initial set of participants, 28 (12%) of 229 patients and 18 (5%) of 353 controls were homozygotes for MBL codon variants (odds ratio 2.59 [95% CI 1.39-4.83], p=0.002). Neither heterozygosity for these codon variants nor the promoter polymorphism was associated with susceptibility. In a confirmatory study, 11 (10%) of 108 patients were MBL homozygotes compared with 36 (5%) of 679 controls (p=0.046).

INTERPRETATION

Homozygotes for MBL codon variants, who represent about 5% of north Europeans and north Americans and larger proportions of populations in many developing countries, could be at substantially increased risk of invasive pneumococcal disease.

Site-specific recombination with the chromosomal tRNA(Leu) gene by the large conjugative Haemophilus resistance plasmid

Characterization of the sequences involved in recombination of the Haemophilus plasmid p1056 with the Haemophilus influenzae chromosome produced evidence indicating site-specific recombination with chromosomal tRNA(Leu). attP sequences identical to those of p1056 were found in six plasmids of diverse origin, suggesting that a family of Haemophilus plasmids recombines with chromosomal tRNA(Leu).

Invasive pneumococcal disease in England and Wales: vaccination implications

Knowledge of the epidemiology of invasive pneumococcal disease (IPD) will aid in planning the use of pneumococcal vaccines. A United Kingdom (UK)-based surveillance in England and Wales (1995-1997) of 11,528 individuals with IPD and a local enhanced surveillance in the Oxford (UK) area (1995-1999) have been analyzed. IPD has a high attack rate in children, with 37.1-48.1 cases per 100,000 infants <1 year old per year, and in older persons, with 21.2-36.2 cases per 100,000 persons >65 years old per year, for England, Wales, and Oxford. The 7-valent conjugate vaccine includes serotypes causing < or =79% of IPD in children <5 years old, but only 66% in adults >65 years old. The data also indicate that IPD varies by serotype, age, and country, emphasizing that the epidemiology of IPD is heterogeneous and requires continued surveillance.

Molecular typing of bacteria directly from cerebrospinal fluid

Using Streptococcus pneumoniae as an example, the ability of multilocus sequence typing (MLST) to characterise isolates directly from cerebrospinal fluid (CSF) was investigated. A nested multiplex polymerase chain reaction method that amplifies the seven housekeeping gene fragments used for pneumococcal MLST was applied to 30 CSF samples from suspected cases of bacterial meningitis. The fragments were amplified from all 14 samples from which Streptococcus pneumoniae was cultured, and, after direct sequencing, the allelic profiles obtained from ten of the samples corresponded to those of clones previously associated with invasive pneumococcal disease. MLST could also predict the penicillin susceptibility and serotype of the CSF isolates.

Epidemiological studies of large resistance plasmids in Haemophilus

The distribution of large conjugative Haemophilus influenzae plasmids in the nasopharyngeal haemophili of a group of people and in a large collection of 541 H. influenzae type b (Hib) isolates was studied. A newly developed PCR-based assay was used to detect the plasmids. The target sequences were chosen from sequence analysis of part of p1056, a large multiresistance plasmid isolated from a clinical Hib isolate, 1056. Fifty-nine per cent of people were found to carry beta-lactamase-positive (beta-lac(+)), ampicillin-resistant (ampR) haemophili with detectable plasmid sequences. Of these, 83% were in Haemophilus parainfluenzae and 17% were in H. influenzae. In the collection of 541 Hib, antibiotic resistance [beta-lac(+)ampR, beta-lac(+)ampR plus tetracycline resistance (tetR) or tetR] was highly correlated with large plasmids. It was found that 2.3% of the isolates contained large cryptic plasmids (i.e. these isolates were susceptible to antibiotics). The distribution of plasmids between invasive and carried Hib did not differ significantly (25 of 245 and 23 of 276, respectively). Isolates with large plasmids occur at high frequency in the nasopharynx of the normal human population and consist of two populations in Hib, one associated with specific antibiotic resistance traits and the other cryptic. These plasmids do not appear to influence the invasiveness of Hib.

Outcome following staphylococcal peritonitis

OBJECTIVE

Staphylococcus spp predominate as the causative pathogen of continuous ambulatory peritoneal dialysis (CAPD)-related peritonitis.This study evaluated the difference in morbidity and mortality between peritonitis caused by S. aureus and coagulase-negative staphylococci (CoNS).

DESIGN

Prospective observational study.

SETTING

A single regional dialysis unit in a teaching hospital.

PATIENTS

Thirty-seven patients had S. aureus peritonitis and 65 patients had CoNS peritonitis between July 1990 and November 1995.

MAIN OUTCOME MEASURES

Using the first recorded episode of peritonitis, survival analysis was performed for time to (1) death, (2) removal of peritoneal dialysis catheter, and (3) change to hemodialysis. Abdominal complications were recorded for the first and subsequent episodes.

RESULTS

No difference in time to death was demonstrated for the two groups (p = 0.79), although two deaths that occurred during therapy for peritonitis were attributable to S. aureus infection. In addition, 5 patients developed serious abdominal complications related to an episode of S. aureus peritonitis. Patients with S. aureus peritonitis had a shorter time to both peritoneal dialysis catheter removal (p = 0.004) and change to hemodialysis (p = 0.014). The change in mode of dialysis was independent of catheter loss.

CONCLUSION

This study highlights the serious nature of S. aureus peritonitis and confirms the need for effective preventive measures against infection by this pathogen.

Prospective evaluation of criteria for microbiological diagnosis of prosthetic-joint infection at revision arthroplasty. The OSIRIS Collaborative Study Group

A prospective study was performed to establish criteria for the microbiological diagnosis of prosthetic joint infection at elective revision arthroplasty. Patients were treated in a multidisciplinary unit dedicated to the management and study of musculoskeletal infection. Standard multiple samples of periprosthetic tissue were obtained at surgery, Gram stained, and cultured by direct and enrichment methods. With reference to histology as the criterion standard, sensitivities, specificities, and likelihood ratios (LRs) were calculated by using different cutoffs for the diagnosis of infection. We performed revisions on 334 patients over a 17-month period, of whom 297 were evaluable. The remaining 37 were excluded because histology results were unavailable or could not be interpreted due to underlying inflammatory joint disease. There were 41 infections, with only 65% of all samples sent from infected patients being culture positive, suggesting low numbers of bacteria in the samples taken. The isolation of an indistinguishable microorganism from three or more independent specimens was highly predictive of infection (sensitivity, 65%; specificity, 99.6%; LR, 168.6), while Gram staining was less useful (sensitivity, 12%; specificity, 98%; LR, 10). A simple mathematical model was developed to predict the performance of the diagnostic test. We recommend that five or six specimens be sent, that the cutoff for a definite diagnosis of infection be three or more operative specimens that yield an indistinguishable organism, and that because of its low level of sensitivity, Gram staining should be abandoned as a diagnostic tool at elective revision arthroplasty.

Positive intravenous line tip cultures as predictors of bacteraemia

Intravenous line tip cultures provide valuable information when taken in conjunction with blood culture, but in practice are often performed in isolation. This retrospective study has evaluated: (1) the frequency of isolated line tip culture; and (2) whether the species of microorganism isolated from line tip culture, using the Maki semi-quantitative culture method, is predictive of bacteraemia. Of 2753 line tip culture episodes in 1659 patients between May 1993 and August 1995, 2230 were performed in isolation (81%). Evaluation of 792 positive line tip culture episodes in 654 patients where blood cultures were performed in the period from 48 h before, to 24 h after tip culture, identified 825 line tip isolates. Of these, 194 were associated with a blood culture positive for the same species. The rate of positive blood culture, according to species, ranged from 10-72%. The highest rate was seen for methicillin-susceptible Staphylococcus aureus where 70 of 97 line tip episodes (72%) were associated with positive blood culture. This compared with a rate of 17% for coagulase-negative staphylococci (P < 0.0001). Patients with line tip cultures positive for S. aureus should be considered to be at high risk of bacteraemia.

Multiple antibiotic resistance in Streptococcus pneumoniae

Streptococcus pneumoniae remains a major pathogen responsible for high morbidity and mortality in both the developed and developing world. During the last few years there has been a dramatic increase in the incidence of penicillin-resistant and multiply antibiotic-resistant pneumococci, and the emergence of isolates with high-level resistance to extended-spectrum cephalosporins. In several countries, 50-80% of pneumococcal isolates, including the great majority of isolates of the serotypes associated with disease and carriage in children, are penicillin-resistant. Penicillin-resistant pneumococci are diverse, but in several countries successful highly penicillin-resistant clones (which in most cases are resistant also to tetracycline, chloramphenicol, and cotrimoxazole, and increasingly to erythromycin) have emerged, and some of these have spread globally. The effect of antibiotic resistance on the clinical outcome of otitis media, pneumonia and meningitis, and the potential of the new conjugate vaccines for controlling pneumococcal disease, are discussed.

Antibody persistence and Haemophilus influenzae type b carriage after infant immunisation with PRP-T

OBJECTIVES

To assess the persistence of serum Haemophilus influenzae type b antibodies and the prevalence of H influenzae type b carriage in a group of preschool age children previously vaccinated in infancy.

DESIGN

Names were randomly selected from immunisation records. Families were visited on five occasions over a period of 12 months and throat swabs were taken from all family members present, with blood obtained from children at the first and last visits.

RESULTS

One hundred and fifty three children at a median age of 3.6 years had a geometric mean titre (GMT) of 1.06 micrograms/ml (95% CI 0.80 to 1.38). Eight per cent had an undetectable antibody concentration, received a booster dose of plain PRP vaccine, and responded with concentrations > 2 micrograms/ml. GMT at 4.5 years of age was 0.89 microgram/ml (0.69 to 1.16). Twelve children who had been exposed to H influenzae had a GMT of 4.7 v 0.8 micrograms/ml for those without exposure.

CONCLUSIONS

Accelerated immunisation against H influenzae without a second year booster results in persistence of satisfactory serum concentrations of antibody to 4.5 years of age. In those with undetectable antibody, immunological memory may still be present.

A molecular analysis of Greek and UK Haemophilus influenzae conjugative resistance plasmids

Antibiotic resistance in Haemophilus influenzae has been associated with the presence of large, chromosomally integrated, conjugative plasmids. The plasmids of 10 beta-lactamase-positive, ampicillin-resistant strains, two from the UK and eight from Greece, were investigated. Plasmids were detected and isolated after transfer to a rec-deficient recipient. Purified whole plasmid was used as probe. In addition a 12 kb PstI fragment containing the putative point of recircularization in one plasmid, p1056, was cloned and used as a probe. All plasmids shared a high degree of sequence homology suggesting that plasmids of diverse geographical origin are highly related. All plasmids also shared sequence homology with the 12 kb PstI fragment containing the point of recircularization, suggesting that the sequences involved in excision and recircularization are conserved.

Methicillin susceptibility testing of staphylococci by Etest and comparison with agar dilution and mecA detection

The susceptibility to methicillin of 44 Staphylococcus aureus and 120 coagulase-negative staphylococci (CNS) was determined by Etest, agar dilution and presence of the mecA gene. There was agreement between the results of all methods when testing S. aureus. However, discrepancies occurred with CNS when cultural methods were compared with presence of the mecA gene. mecA-positive isolates tested as resistant more often with agar dilution on Columbia agar plus 5% NaCl than by Etest.

Native-valve endocarditis caused by Staphylococcus lugdunensis

Coagulase-negative staphylococci cause about 5% of native-valve endocarditis. Staphylococcus lugdunensis, a recently-described species of coagulase-negative staphylococci, has been reported to cause destructive native-valve endocarditis with a high mortality. We report four consecutive cases of definite Staphylococcus lugdunensis native-valve endocarditis by the Duke criteria over a 4-year period. All patients required urgent aortic valve replacement 1-5 days after admission, and recovered. An intriguing, aspect in the presentation of these patients was a history of vasectomy and inguinal skin breaks in the immediate period preceding the occurrence of endocarditis.

Safe intravenous antibiotic therapy at home: experience of a UK based programme

Outpatient i.v. antibiotic therapy is well developed in the United States, largely because of pressures from third-party payers to reduce costs of medical care. We have developed an outpatient i.v. antibiotic programme in Oxford, that has evolved from a desire to provide high quality i.v. therapy to AIDS patients with cytomegalovirus retinitis. We describe the rationale of the service and report on our first two years' experience. We treated 67 consecutive patients (eight with HIV infection) at home with i.v. antibiotics. This resulted in a saving of 2275 hospital days for those patients without HIV infection. HIV positive patients received 69 months of home i.v. therapy. Minor intravascular catheter complications occurred in only five patients (7.5%). The only serious complications were three episodes of catheter-related sepsis (4.5%), all occurring in AIDS patients who had lines in for more than six months. We have shown that home i.v. antibiotic therapy can be delivered safely to patients with a wide variety of infectious problems using the existing network of community nurses in the National Health Service. Essential components to the programme include a multidisciplinary team working between the hospital and community and a written shared care protocol. Such a programme can result in reduced lengths of hospital stay and patient, community nurse and physician satisfaction.

Carriage of Haemophilus influenzae and Streptococcus pneumoniae in healthy Chinese and Vietnamese children in Hong Kong

Nasopharyngeal carriage of Haemophilus influenzae and Streptococcus pneumoniae was studied in 621 healthy Chinese children and 300 healthy Vietnamese children aged from 2 months to 5 years in Hong Kong. The carriage rate of H. influenzae type b in Vietnamese children was 1.3% (CI 0.04-2.63); it was zero in Chinese. The carriage rate of non-typable H. influenzae was 5.8% (CI 1.4-7.6%) in Chinese and 65.4% (CI 58.9-69.8%) in Vietnamese. The carriage rates of S. pneumoniae were 10.8% (CI 8.3-13.2%) and 55.7% (CI 50.1-61.3%) in Chinese and Vietnamese children, respectively. Univariate and multivariate logistic regression analyses were performed to search for factors associated with differences in carriage rates of both H. influenzae and S. pneumoniae between Chinese and Vetnamese children. Although older age, smaller living area and parental smoking were associated with higher carriage rates, these could not explain the remarkably low carriage rates of both bacteria in Chinese children.

The elucidation of novel capsular genotypes of Haemophilus influenzae type b with the polymerase chain reaction

Molecular characterization is an important pre-requisite for post-vaccine studies of Haemophilus influenzae type b (Hib). Three capsular genotyping patterns, b(S), b(G) and b(V), have been described in the major phylogenetic lineage of Hib. However, in a recent series of prospective studies, three new hybridisation patterns were observed among 425 strains of Hib. Four pairs of polymerase chain reaction (PCR) primers were used to identify the capsular gene (cap) structure of these Hib strains. This showed that the strains possessed simple DNA re-arrangements. In two instances a change in restriction enzyme recognition site was the most likely cause of the new hybridisation pattern. The third strain possessed a cap b locus consisting of intact tandem repeats of cap b in a b(S) background. It was reasoned that a similar cap b locus would not be readily recognised by hybridisation in a b(G) background, and b(G) strains were therefore characterized by the PCR method. This showed one of 35 b(G) strains to possess a cap locus with intact tandem repeat copies of cap b. The novel capsular genotypes described here are rare, but can be detected rapidly and accurately by a combination of PCR and capsular genotyping hybridisation patterns.