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David R Murdoch

Publications and source records attributed to David R Murdoch.

At least 19 recordsLinked to original sources
PubMed2007

Comparison of the NOW Influenza A & B, NOW Flu A, NOW Flu B, and Directigen Flu A+B assays, and immunofluorescence with viral culture for the detection of influenza A and B viruses.

To evaluate the Binax NOW Influenza A & B combination assay, we tested upper respiratory tract samples in parallel with the Binax NOW Flu A and Binax NOW Flu B assays, the Becton-Dickinson Directigen Flu A+B assay, and immunofluorescence, and the results were compared with viral culture. Of the 521 samples tested, influenza A was cultured from 113 and influenza B from 6. There were no significant differences in the performance of all rapid antigen tests, with sensitivities of 53% to 59% for detecting influenza A compared with culture and immunofluorescence (80%). The sensitivities for all rapid tests were significantly higher for nasopharyngeal samples than for throat swabs. The Binax NOW Influenza A & B assay performed as well as other rapid assays. Commercial antigen detection assays are useful tools for the rapid diagnosis of influenza; however, confirmatory testing is always recommended. The use of nasopharyngeal samples for all rapid detection methods should be strongly encouraged.

Adolescent↗
PubMed2006

Emergence of Salmonella enterica serotype Paratyphi A as a major cause of enteric fever in Kathmandu, Nepal.

We performed pulsed-field gel electrophoresis (XbaI) on 114 bloodstream isolates of Salmonella enterica serotype Paratyphi A and S. enterica serotype Typhi collected from febrile patients in Kathmandu, Nepal. Of the 56 S. Paratyphi A isolates, 51 (91%) were indistinguishable, which suggests the emergence of a single clone. In contrast, only 21 (36%) of the 58 S. Typhi isolates exhibited a common genotype, which is consistent with endemic disease from multiple sources.

Adolescent↗
PubMed2006

The rapid evaluation of bacterial growth and antibiotic susceptibility in blood cultures by selected ion flow tube mass spectrometry.

We have measured the production of volatile organic compounds (VOCs) by selected ion flow tube mass spectrometry (SIFT-MS) in the headspaces of conventional BacT/ALERT blood culture bottles (Biomerieux, Durham, NC) artificially infected with 5 bacterial strains. Uninfected blood samples were inoculated with Pseudomonas aeruginosa, Staphylococcus aureus, Streptococcus pneumoniae, Escherichia coli, and Neisseria meningitidis. Growth and species identification were determined at 6 h by measuring a panel of 9 VOC products. Two species, E. coli and S. aureus, were also incubated in the presence of gentamicin or flucloxacillin, respectively, above or below their demonstrated MIC. The concentration-dependent antibiotic susceptibility of both strains was demonstrated by the inhibition of VOC production at 22 h (P < .05). These results suggest incorporating SIFT-MS detection of microbial VOCs as a sensitive method for bacterial detection, identification, and determination of antibiotic susceptibility in a conventional blood culture system.

Bacteremia↗
PubMed2006

Characteristics of Streptococcus pseudopneumoniae isolated from purulent sputum samples.

Streptococcus pseudopneumoniae is a recently described streptococcus that is phenotypically and genetically distinct from Streptococcus pneumoniae and other viridans streptococci. Key characteristics of S. pseudopneumoniae are the absence of a pneumococcal capsule, insolubility in bile, resistance or indeterminate susceptibility to optochin when incubated in 5% CO2 but susceptibility to optochin when incubated in ambient air, and a positive reaction with the AccuProbe DNA probe hybridization test. The clinical importance of this bacterium is currently unknown. We report the characteristics and associated clinical data of 35 strains of S. pseudopneumoniae isolated from sputum samples from 33 patients. All isolates produced a positive result with the NOW S. pneumoniae antigen test (Binax, Inc.). No isolate was resistant to penicillin, but 60% were resistant to erythromycin and 77% were resistant to tetracycline. All patients had lower respiratory tract symptoms, 79% had chronic obstructive pulmonary disease (COPD), and 33% had chest radiographic infiltrates. Compared with matched control patients who had Streptococcus pneumoniae isolated from sputum, patients with S. pseudopneumoniae infection were more likely to have a history of COPD (odds ratio [OR], 5.0; 95% confidence interval [CI], 1.67 to 20.11) or exacerbation of COPD (OR, 6.5; 95% CI, 2.61 to 16.20). Further research is needed to better characterize the epidemiology of S. pseudopneumoniae colonization and the role of S. pseudopneumoniae in COPD and other diseases.

Adolescent↗
PubMed2005

Detection of volatile metabolites produced by bacterial growth in blood culture media by selected ion flow tube mass spectrometry (SIFT-MS).

To achieve faster bacteremia diagnosis, selected ion flow tube mass spectrometry (SIFT-MS) measured metabolic gases in the headspaces of BacT/ALERT blood culture bottles. Pseudomonas aeruginosa, Streptococcus pneumoniae, Escherichia coli, Staphylococcus aureus and Neisseria meningitidis growth and trace gas patterns were detected from 10 colony forming units after 6 h.

Bacteremia↗
PubMed2005

Enteric (typhoid) fever in travelers.

The incidence of enteric (typhoid) fever in travelers is estimated to be approximately 3-30 cases per 100,000 travelers to developing countries. Recently, it is become clear that travelers who are visiting friends and relatives, especially travelers to the Indian subcontinent, seem to be the most vulnerable to enteric fever and require special attention for prevention. Recent concerns are the increasing incidence of paratyphoid fever in Asia, which is not covered by available typhoid vaccines, and the emergence of infections caused by antibiotic-resistant strains (including strains resistant to fluoroquinolones). Typhoid vaccination is recommended for most travelers to moderate- to high-risk countries. Because of the nonspecific clinical presentation of enteric fever, a high index of suspicion is important in febrile travelers who have traveled to areas of endemicity.

Bacterial Vaccines↗
PubMed2005

Comparison of PCR-ELISA and galactomannan detection for the diagnosis of invasive aspergillosis.

AIM: To compare PCR with galactomannan antigen detection for the diagnosis of invasive aspergillosis (IA). METHODS: We prospectively collected serial blood samples from haematological patients at risk of IA, and analysed their samples retrospectively for galactomannan (GM) antigen using the Platelia test and for aspergillus DNA using an in-house PCR-ELISA assay. Matched GM and PCR analyses were performed on 263 samples from 25 patients. Patients were classified for potential IA according to international consensus criteria, with five patients classified as positive (four proven, one probable) and 20 classified as negative (seven possible, 13 no evidence IA). RESULTS: All five patients with IA were positive by PCR with positive results in 24 of 82 samples, whereas three of five patients were positive by GM with four of 82 samples being positive. Three of 20 patients without IA were positive by PCR in 18 of 181 samples, whereas corresponding results for GM detection were one of 20 and one of 181, respectively. Adjustment of ELISA cut-off values and/or the requirement for two consecutive samples to be positive generated different results; however, lowering the positivity index (PI) for GM detection to 0.5 did not improve the sensitivity of the assay. Optimal results for PCR detection and GM were: 100% and 60% sensitivity, 85% and 95% specificity, 0.625 and 0.75 positive predictive value, and 1.0 and 0.8 negative predictive value, with a false-positive sample rate of 8 and 0.4%, positive likelihood ratio of 6.66 and 11.99 and negative likelihood ratio of 0 and 0.42, respectively. CONCLUSIONS: This PCR method is very sensitive for the diagnosis of IA but is associated with a moderate rate of false positives; the GM assay exhibited poor sensitivity but high specificity. Further evaluation of PCR assays for the diagnosis of IA and other invasive fungal infections is warranted.

Adolescent↗
PubMed2005

Clinical profile and strain relatedness of recurrent enterococcal bacteremia.

We defined the molecular epidemiology of recurrent enterococcal bacteremia using pulsed field gel electrophoresis. We identified 27 patients, comprising 60 episodes; strain relatedness was demonstrated in 8 patients with isolates separated by up to 6 y. Carriage of pathogenic enterococci may be prolonged, although re-infection with novel strains is more commonly seen.

Adolescent↗
PubMed2005

Statistical models of acute mountain sickness.

Acute mountain sickness (AMS) is caused by exposure to altitudes exceeding 2500 m and often resolves by acclimatization without further ascent. Statistical models of AMS score and the probability of an AMS diagnosis were developed to allow the combination of dissimilar exposures for simultaneous analysis. The study population was 302 trekkers from a previous investigation who provided self-reported symptoms upon arrival at 3840 m during hikes through altitudes of 1500 to 6200 m. AMS score (Hackett scale) was estimated by linear regression and the probability of an AMS diagnosis (Lake Louise criteria) by logistic regression. AMS score or probability was significantly associated with exposure day and altitude. Increased altitude over the prior 3 days resulted in higher estimated AMS score or probability and decreased altitude in lower score or probability. The odds ratio (OR) of AMS was 3.6 if not on acetazolamide. Females appeared slightly more susceptible than males (1.5 OR). The approach offers the advantages of (1) improved statistical power by combining exposures, (2) insight into the dose-response relationship of altitude exposure and AMS risk, (3) quantitative tests for the significance of factors that might affect AMS susceptibility, and (4) practical tools to track individual climbers and plan operational ascents.

Acclimatization↗
PubMed2004

A new phenotype of resistance to lincosamide and streptogramin A-type antibiotics in Streptococcus agalactiae in New Zealand.

OBJECTIVES: To characterize a new type of resistance to clindamycin in Streptococcus agalactiae. METHODS: Nineteen erythromycin-susceptible, clindamycin-resistant S. agalactiae isolates from New Zealand were studied. MICs of macrolide, lincosamide and streptogramin antibiotics were determined. Clindamycin and streptogramin resistance genes were searched for by PCR. Isolates were compared by serotyping and by DNA macrorestriction patterns determined by PFGE. Conjugative transfer of resistance traits to recipient strains of S. agalactiae and Enterococcus faecium was assayed. RESULTS: The 19 S. agalactiae isolates were intermediate or resistant to clindamycin (MIC range: 0.5-2 mg/L) and lincomycin (MIC range: 1-8 mg/L) and had high MICs of dalfopristin (4-32 mg/L), a streptogramin A-type antibiotic, compared with controls. By contrast, the strains were susceptible to macrolides and quinupristin, a streptogramin B-type antibiotic. This new phenotype was called LSA (lincosamide-streptogramin A). Clindamycin resistance could not be transferred to recipient strains. Thirteen isolates belonged to serotype III and to a single PFGE genotype A, and five isolates belonged to serotype I and to genotype B. One isolate was non-typeable and belonged to a distinct genotype C. CONCLUSIONS: We have characterized a new LSA phenotype in S. agalactiae. Analysis of restriction patterns of S. agalactiae chromosomal DNA showed that the resistance was spread in a minimum of three bacterial clones. The genetic and biochemical basis for the resistance remains unknown.

Adult↗
PubMed2004

Detection of Campylobacter species in faecal samples by direct Gram stain microscopy.

AIMS: To evaluate the Gram stain with carbol-fuchsin counterstain for the rapid detection of Campylobacter species in faecal samples. METHODS: In total, 842 consecutive diarrhoeic faecal samples were prospectively examined for Campylobacter species by Gram stain and culture. RESULTS: Campylobacter species were isolated from 84 faecal samples (all Campylobacter jejuni). Compared with culture, Gram stain microscopy had a sensitivity of 89%, specificity of 99.7%, positive predictive value of 97%, and negative predictive value of 99% for detecting Campylobacter species. CONCLUSIONS: The direct Gram stain method can provide a presumptive result within 30 minutes of receipt of a faecal sample in the laboratory with relatively high sensitivity, and at low cost. Laboratories in areas where Campylobacter enteritis is common and/or with limited resources for Campylobacter culture should consider adopting this as a routine method.

Adolescent↗
PubMed2004

Viral etiology of acute respiratory tract infections in children presenting to hospital: role of polymerase chain reaction and demonstration of multiple infections.

BACKGROUND: Viral lower respiratory tract infections are a leading cause of hospitalization for young children. METHODS: We used polymerase chain reaction (PCR) and conventional methods of cell culture and antigen detection to establish the viral etiology of acute respiratory tract infections in 75 hospitalized children. RESULTS: One or more viral pathogens were detected in 65 (87%) children, with respiratory syncytial virus being the most commonly identified virus (36 children). Other viruses identified included influenza virus types A and B, parainfluenzavirus type 3, adenovirus, enterovirus, rhinovirus, coronavirus and human metapneumovirus. PCR increased the diagnostic yield significantly compared with antigen detection and culture, with 39 (21%) diagnoses identified by this method. Multiple infections were identified in 20 (27%) children. CONCLUSIONS: PCR-based methodologies offer increased sensitivity for the detection of most respiratory viruses in young children. The inclusion of PCR into diagnostic testing strategies is needed to broaden our understanding of the natural ecology of respiratory viruses and the significance of multiple infections.

Acute Disease↗