David R Murdoch

University of Otago, Taieri, Otago Region, New Zealand

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Publications (159)807.51 Total impact

  • Clinical infectious diseases : an official publication of the Infectious Diseases Society of America. 11/2014;
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    ABSTRACT: Several commercial assays are now available to detect the nucleic acid of multiple respiratory pathogens from a single specimen. Head-to-head comparisons of such assays using a single set of standard specimens provide additional information about key assay parameters such as sensitivity, specificity and lower limits of detection, and help to inform the decision regarding which method to use. We evaluated two real-time PCR platforms: the Fast-track Diagnostics® (FTD) multiplex respiratory panel and a TaqMan array card (TAC) for simultaneous uniplex detection of multiple respiratory pathogens. Two sets of samples were used to evaluate the assays. One set was created by spiking pooled nasal wash or phosphate buffered saline with specified volumes of known concentrations of virus and/or bacteria. Clinical nasal wash specimens from children with lower respiratory tract illness comprised the other set. Thirteen pathogen targets were compared between the two platforms. Testing with a validation panel of spiked samples revealed a sensitivity of 96.1% and 92.9% for the FTD and TAC assays, respectively. Specificity could not be reliably calculated due to a suspected contamination of the sample substrate. Inter-assay agreement was high (>95%) for most targets. Previously untested clinical specimens tested by both assays revealed a high percent agreement (>95%) for all except rhinovirus, enterovirus and Streptococcus pneumoniae. Limitations of this evaluation included extraction of the validation samples by two different methods and the evaluation of the assays in different laboratories. However, neither of these factors significantly impacted inter-assay agreement for these sets of samples, and it was demonstrated that both assays could reliably detect clinically relevant concentrations of bacterial and viral pathogens. Copyright © 2014. Published by Elsevier B.V.
    Journal of microbiological methods. 10/2014; 107C:222-226.
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    ABSTRACT: AimThis study aims to describe the microbiology of middle ear fluid (MEF) in a cohort of children vaccinated with Streptococcus pneumoniae conjugate vaccine (PCV7) having ventilation tube insertion. Nasopharyngeal (NP) carriage of otopathogens in these children is compared with children without history of otitis media.Methods Between May and November 2011, MEF and NP samples from 325 children aged <3 years were collected in three major centres in New Zealand at the time of ventilation tube insertion. An age-matched non-otitis-prone comparison group of 137 children had NP samples taken. A questionnaire was completed by both groups.ResultsImmunisation coverage with at least one dose of PCV7 was 97%. Haemophilus influenzae was cultured in 19.4% of MEF and was polymerase chain reaction (PCR) positive in 43.4%. S. pneumoniae and Moraxella catarrhalis were cultured in <10% of MEF samples but were PCR positive for 23.1% and 38.7%, respectively. H. influenzae was the most common organism isolated from NP samples (60%) in the grommet group, while M. catarrhalis (56%) was the most common in the non-otitis prone group. S. pneumoniae was more commonly found in the nasopharynx of children with ear disease (41% vs. 29%). 19F was the most prominent S. pneumoniae serotype in NP samples of both groups, but no serotype dominated in MEF. Ninety-five per cent of H. influenzae isolates were confirmed to be non-typeable H. influenzae.Conclusion In this cohort of children with established ear disease requiring surgical intervention, non-typeable H. influenzae is the dominant pathogen in both the nasopharynx and MEF.
    Journal of Paediatrics and Child Health 10/2014; · 1.25 Impact Factor
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    ABSTRACT: Data regarding characteristics of bloodstream infections in Myanmar are limited.
    Transactions of the Royal Society of Tropical Medicine and Hygiene 09/2014; · 1.82 Impact Factor
  • Clinical Infectious Diseases 07/2014; · 9.37 Impact Factor
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    ABSTRACT: Previous randomized controlled trials of vitamin D supplementation and blood pressure (BP) mainly have given vitamin D for short periods (<6 months) or at low doses (400 IU per day). This study aims to determine whether long-term high-dose vitamin D taken for 18 months lowers BP. Adults were recruited from a healthcare organization or university into a double-blind controlled trial and randomized to receive either vitamin D3 200 000 IU for 2 months followed by 100 000 IU monthly up to 18 months (n=161) or placebo (n=161). BP was measured at baseline, 5, and 18 months. Subjects had a mean (SD) age of 47.6 (9.7) years, 75% were women, and 94% were of European ancestry (white). Mean (SD) 25-hydroxyvitamin D3 changed from 73 (22) nmol/L at baseline to 124 (28) nmol/L at 18 months in the vitamin D group, and from 71 (22) nmol/L to 56 (22) nmol/L in the placebo group. Mean BP was similar for the vitamin D and placebo groups at baseline (123.4/76.3 versus 122.6/75.6 mm Hg; respectively). The mean change (95% confidence interval) in BP at 18 months minus baseline in the vitamin D group compared with placebo group was -0.6 (-2.8 to 1.6) mm Hg for systolic (P=0.61) and 0.5 (-1.1, 2.2) mm Hg for diastolic (P=0.53). Long-term vitamin D supplementation, which increased mean 25-hydroxyvitamin D3 concentration >100 nmol/L for 18 months, had no effect on systolic or diastolic BP in predominantly white, healthy adults without severe vitamin D deficiency. Beneficial effects on BP cannot be ruled out for other populations.
    Hypertension 06/2014; · 6.87 Impact Factor
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    ABSTRACT: Vitamin D deficiency is associated with infectious diseases; however, it is not known whether vitamin D levels are affected by acute infection. Our aim was to establish whether 25-hydroxyvitamin D (25OHD) levels taken during an acute bacterial infection are representative of baseline levels.
    Journal of Paediatrics and Child Health 06/2014; · 1.25 Impact Factor
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    ABSTRACT: Streptococcus pseudopneumoniae is a novel species belonging to the viridans group streptococci (VGS). Accurate species identification is challenging due to significant homology to other VGS. Whole-genome sequencing of S. pseudopneumoniae suggests it most likely originated from Streptococcus pneumoniae, sharing many of its virulence genes. There are several limitations when using traditional phenotypic identification methods to identify this organism. Other identification approaches include genotypic methods, pherotype analysis, and matrix-assisted laser desorption ionization–time of flight mass spectrometry. S. pseudopneumoniae is most commonly isolated from respiratory specimens, and its associations with chronic obstructive pulmonary disease and aspiration pneumonia have been previously described, suggesting that the organism treads the fine line between commensal and pathogen. Recent isolation of S. pseudopneumoniae from blood raises the important question of its clinical relevance. Antimicrobial susceptibility profiles of S. pseudopneumoniae indicate a higher level of resistance than other VGS. However, further information may be required to determine the choice of breakpoints.
    Clinical Microbiology Newsletter 05/2014; 36(9):65–71.
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    ABSTRACT: We retrospectively examined medical records of 87 patients with HACEK bacterbaemia to determine whether endocarditis was present as defined by the Duke criteria. The overall positive predictive value (PPV) of HACEK bacteraemia for endocarditis was 60%. The PPV varied with different HACEK species from 0% (Eikenella corrodens) to 100% (Aggregatibacter actinomycetemcomitans).
    Journal of Medical Microbiology 03/2014; · 2.30 Impact Factor
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    ABSTRACT: The International Collaboration on Endocarditis Prospective Cohort Study (ICE-PCS) collected worldwide data on the presentation, management and outcome of infective endocarditis (IE). We present data from patients with endocarditis enrolled from New Zealand. Patients who fulfilled the Duke criteria for definite or probable endocarditis were enrolled from five district health boards: Auckland, Counties Manukau, Waitemata, Capital and Coast, and Canterbury, between June 2000 and September 2005. There were 336 New Zealand patients enrolled in the ICE-PCS. Prosthetic valve endocarditis occurred in 31%. Underlying medical conditions were present in 28% of patients, but only 4% of patients had rheumatic heart disease. Forty patients (12%) had healthcare-associated endocarditis. Viridans streptococci were the most common cause of IE (32%), followed by Staphylococcus aureus (24%). Patients with S. aureus IE were more likely to present within a week of symptom onset than those with viridans streptococcus IE (OR 4.18, 95% CI 2.36-7.42). Surgery was performed in 33% of patients. In total, 20 patients (6%) died in hospital. Those with endocarditis caused by coagulase-negative staphylococci had an increased risk of death compared with those viridans streptococcus endocarditis (RR 4.7, 95% CI 1.2-17). The risk of stroke was higher in those with endocarditis caused by S. aureus and coagulase-negative staphylococci (RR 2.7, 95% CI 1.2-6.05, and 4.9, 95% CI 1.9-13, respectively). While viridans streptococci remain the predominant causative organisms of IE in New Zealand, many 'traditional' clinical and management aspects of this disease no longer apply. This paper provides a reference for local practitioners assessing and managing IE.
    The New Zealand medical journal 01/2014; 127(1391):38-51.
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    ABSTRACT: Pneumococcal disease is a significant cause of morbidity and mortality in young children in Nepal, and currently available pneumococcal conjugate vaccines offer moderate coverage of invasive disease isolates.
    PLoS ONE 01/2014; 9(6):e98739. · 3.53 Impact Factor
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    ABSTRACT: To determine whether supplementation with vitamin D improves resilience to the adverse effects of earthquakes. Opportunistic addition to an established randomised double blind placebo controlled trial. Christchurch, New Zealand, where a prolonged series of catastrophic earthquakes beginning on 4 September 2010 occurred, which caused widespread destruction, fatalities, and extensive psychological damage. 322 healthy adults (241 women; 81 men) aged 18-67 who were already participating in the vitamin D and acute respiratory infections study (VIDARIS) between February 2010 and November 2011. Participants were randomised to receive an oral dose of either 200 000 IU vitamin D3 monthly for two months then 100 000 IU monthly (n=161) or placebo (n=161) for a total of 18 months. This is a post hoc analysis from the previously published VIDARIS trial. The primary endpoint in the current analysis was the self reported effects and overall adverse impact of the Christchurch earthquakes as assessed by questionnaire four months after the most destructive earthquake on 22 February 2011, which was used as the index event. The secondary end point was the number of "psychological" adverse events that participants reported at their usual monthly appointments as part of the original VIDARIS trial. 308 participants completed the earthquake impact questionnaire (n=152 in the vitamin D group and 156 in the placebo group). There was no significant difference in the number of self reported adverse effects between those receiving vitamin D supplementation and those receiving placebo. There was also no difference in the overall adverse impact score between treatment groups (χ(2) P=0.44). The exception was that those in the vitamin D group experienced more adverse effects on family relationships (22% v 13%; χ(2) P=0.03). The number of psychological adverse events-such as fatigue, stress, anxiety, and insomnia-that participants reported at their usual monthly appointments was significantly higher after the earthquake (χ(2) P=0.007) but did not differ between treatment groups. In this trial, vitamin D supplementation did not reduce the adverse impact of earthquakes in healthy adults. Trial registration Australian New Zealand Clinical Trials Registry (anzctr.org.au) ACTRN12609000486224. © Slow et al 2014.
    BMJ Clinical Research 01/2014; 349:g7260. · 14.09 Impact Factor
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    European Respiratory Journal 12/2013; · 6.36 Impact Factor
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    ABSTRACT: Observational studies have reported an inverse association between serum 25-hydroxyvitamin D (25OHD) concentrations and Staphylococcus aureus nasal carriage; however, clinical trials of vitamin D supplementation are lacking. To assess the effect of vitamin D3 supplementation on persistent S. aureus nasal carriage we conducted a randomized, double-blind, placebo-controlled trial among 322 healthy adults. Participants were given an oral dose of either 200 000 IU vitamin D3 for each of 2 months, followed by 100 000 IU monthly or placebo in an identical dosing regimen, for a total of 18 months. Nasal swabs for S. aureus culture and serum for 25OHD measurement were obtained at baseline, 6, 12 and 18 months of study. The mean baseline concentration of 25OHD was 72 nM (SD 22 nM). Vitamin D3 supplementation increased 25OHD levels which were maintained at >120 nM throughout the study. Nasal colonization by S. aureus was found in 31% of participants at baseline. Persistent carriage, defined as those that had positive S. aureus nasal cultures for all post-baseline swabs, occurred in 20% of the participants but vitamin D3 supplementation was not associated with a reduction in persistent carriage (OR = 1.39, 95% CI 0.63-3.06). Risk factor analysis showed that only gender was significantly associated with carriage, where women were less likely to be carriers than men (relative risk 0.83, 95% CI 0.54-0.99). Serum 25OHD concentrations were not associated with the risk of carriage. In conclusion, monthly administration of 100 000 IU of vitamin D3 did not reduce persistent S. aureus nasal carriage.
    Clinical Microbiology and Infection 07/2013; · 4.58 Impact Factor
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    ABSTRACT: Background. Legionnaires' disease cannot be clinically or radiographically distinguished from other causes of pneumonia, and specific tests are required to make the diagnosis. Currently, testing occurs erratically and, instead, clinicians rely on empiric treatment strategies and ignore public health implications of the diagnosis. We aimed to measure the increase in case detection of legionnaires' disease following the introduction of routine PCR testing of respiratory specimens. PCR is the most sensitive diagnostic tool for legionnaires' disease. Methods. In a quasi-experimental study in Christchurch, New Zealand, we compared the number of hospitalized cases of legionnaires' disease diagnosed during a two-year period before the introduction of a routine PCR testing strategy (November 2008 to October 2010) with a similar period after the introduction (November 2010 to October 2012). With this testing strategy, all respiratory specimens from hospitalized patients with pneumonia sent to the region's sole tertiary-level laboratory were tested for Legionella by PCR, whether requested or not. Results. During November 2008 to October 2010 there were 22 cases of legionnaires' disease compared with 92 during November 2010 to October 2012. Of 1834 samples tested since November 2010, 1 in 20 was positive, increasing to 1 in 9 during peak Legionella season (November to January). Increasing bacterial load was associated with increasing disease severity. Conclusion. In our region, the burden of legionnaires' disease is much greater than was previously recognized. Routine PCR testing provides results within a clinically-relevant time frame and enables improved characterization of the regional epidemiology of legionnaires' disease.
    Clinical Infectious Diseases 07/2013; · 9.37 Impact Factor
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    ABSTRACT: OBJECTIVES: To determine whether systematic testing of faecal samples with a broad range multiplex PCR increases the diagnostic yield in patients with diarrhoea compared with conventional methods and a clinician initiated testing strategy. METHODS: 1758 faecal samples from 1516 patients with diarrhoea submitted to two diagnostic laboratories were tested for viral, bacterial, and parasitic pathogens by Fast-Track Diagnostics multiplex real-time PCR kits and conventional diagnostic tests. RESULTS: Multiplex PCR detected pathogens in 530 samples (30%): adenovirus (51, 3%), astrovirus (95, 5%), norovirus (172, 10%), rotavirus (3, 0.2%), Campylobacter jejuni/coli (85, 5%), Salmonella spp. (22, 1%), Clostridium difficile (72, 4%), entero-haemorrhagic Escherichia coli (21, 1%), Cryptosporidium spp. (3, 0.2%), Entamoeba histolytica (1, 0.1%), and Giardia lamblia (59, 3%). In contrast, conventional testing detected a pathogen in 324 (18%) samples. CONCLUSIONS: Using a systematic approach to the diagnosis of gastroenteritis improved diagnostic yield. This enhanced detection with PCR was achieved by a combination of improved detection of individual pathogens and detection of pathogens not requested or unable to be tested by conventional tests. This approach also allowed earlier identification for most pathogens and created a workflow which is likely to adapt well for many diagnostic laboratories.
    The Journal of infection 04/2013; · 4.13 Impact Factor
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    ABSTRACT: Nucleic acid detection methods are being increasingly used for the diagnosis of Mycobacterium tuberculosis (1).…
    Journal of clinical microbiology 04/2013; · 4.16 Impact Factor
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    ABSTRACT: The Vi capsular polysaccharide (ViPS) protects Salmonella enterica subspecies enterica serotype Typhi (S.Typhi) in vivo by multiple mechanisms. Recent microbiological reports from typhoid endemic countries suggest that acapsulate S.Typhi may occur in nature and contribute to clinical typhoid fever that is indistinguishable from disease caused by capsulate strains. The prevalence and genetic basis of ViPS-negative S.Typhi isolates in children from Kathmandu, Nepal, were tested in 68 isolates. Although 5.9% of isolates tested negative for capsular expression by slide agglutination tests, a novel multiplex PCR assay and individual PCR analyses demonstrated the presence of all 14 genes responsible for the synthesis, transportation and regulation of the ViPS. These data suggest that phenotypically acapsulate S.Typhi may not have a genetic basis for the same.
    Journal of Tropical Pediatrics 04/2013; · 1.01 Impact Factor
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    ABSTRACT: Multiplex PCR has become the test of choice for the detection of multiple respiratory viruses in clinical specimens. However, there are few direct comparisons of different PCR assays. This study compares 4 different multiplex PCR assays for the recovery of common respiratory viruses. We tested 213 respiratory specimens using four different multiplex PCR assays: the xTAG respiratory viral panel fast (Abbott Molecular Laboratories), Fast-track Respiratory Pathogen assay (Fast-track Diagnostics), Easyplex respiratory pathogen 12 kit (Ausdiagnostics), and an in-house multiplex real-time PCR assay. The performance of the four assays was very similar, with 93-100% agreement for all comparisons. Other issues, such as through-put, technical requirements and cost, are likely to be as important for making a decision about which of these assays to use given their comparative performance.
    Journal of virological methods 04/2013; · 2.13 Impact Factor
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    ABSTRACT: A suite of volatiles have previously been identified as specific markers of Mycobacterium tuberculosis metabolism in vitro. These markers - methyl phenylacetate, methyl p-anisate, methyl nicotinate, o-phenylanisole with the addition of methyl salicylate, may also be derived from other sources and confound development of a breath test for tuberculosis. To identify potential sources of these potential biomarkers food products, cosmetics, TB medication, environmental air and cigarette smoke were analysed for these markers using solid phase microextraction coupled with Gas Chromatography/Mass Spectrometry. Breath from healthy subjects, including smokers was also tested. Methyl salicylate was commonly detected, making this unsuitable as a specific marker for M. tuberculosis. Methyl nicotinate was detected repeatedly in cigarettes. Methyl phenylacetate was detected in 1.7% of healthy subjects and o-phenylanisole in just 1% of healthy breath indicating these may be more suitable for inclusion in the tuberculosis breath test due to their low "background" level. These results justify further clinical studies to further explore these markers as specific indicators of M. tuberculosis infection.
    Tuberculosis (Edinburgh, Scotland) 03/2013; · 2.54 Impact Factor

Publication Stats

3k Citations
807.51 Total Impact Points


  • 2003–2014
    • University of Otago
      • • Christchurch School of Medicine and Health Sciences
      • • Department of Microbiology and Immunology
      Taieri, Otago Region, New Zealand
    • Himalayan Rescue Association Nepal
      Kantipura, Central Region, Nepal
  • 2013
    • Auckland City Hospital
      Окленд, Auckland, New Zealand
  • 2009–2013
    • University of Oxford
      • Department of Paediatrics
      Oxford, ENG, United Kingdom
    • Johns Hopkins Bloomberg School of Public Health
      • Department of International Health
      Baltimore, Maryland, United States
    • North Carolina Clinical Research
      Raleigh, North Carolina, United States
  • 2006–2013
    • Canterbury Health Laboratories
      Christchurch, Canterbury Region, New Zealand
  • 1995–2013
    • Canterbury District Health Board
      Christchurch, Canterbury Region, New Zealand
  • 2012
    • Patan Academy of Health Sciences
      Lalitpur, Central Region, Nepal
    • University Medical Center Hamburg - Eppendorf
      • Department of Medical Microbiology, Virology and Hygiene
      Hamburg, Hamburg, Germany
    • Mahidol University
      • Department of Tropical Pathology
      Bangkok, Bangkok, Thailand
  • 2011
    • Oxford University Hospitals NHS Trust
      Oxford, England, United Kingdom
    • Turku University Hospital
      Turku, Province of Western Finland, Finland
  • 1999–2011
    • Duke University
      Durham, North Carolina, United States
  • 2008
    • IDIBAPS August Pi i Sunyer Biomedical Research Institute
      Barcino, Catalonia, Spain
  • 2001–2007
    • Duke University Medical Center
      • • Department of Medicine
      • • Division of Infectious Diseases
      Durham, North Carolina, United States
  • 2002
    • University of Canterbury
      Christchurch, Canterbury Region, New Zealand