Stool PCR may not be a substitute for enrichment culture for the detection of salmonella.

PURPOSE: Polymerase chain reaction (PCR) is increasingly being used to detect enteric pathogens and is currently NICE's recommended practice. We wished to evaluate the performance characteristics of PCR for the detection of salmonella in consecutive stool samples in a real-world setting, compared to the gold standard of enrichment culture. METHODOLOGY: We performed a prospective study over 9 months in which the PCR and culture results for salmonella were scrutinized for all stool samples sent to the laboratory. All stool samples underwent selenite enrichment culture for salmonella with confirmation being obtained using the API 10S and serotyping. Samples also underwent PCR using the BD MAX Enteric Bacterial Panel. The sensitivity and specificity of PCR in detecting salmonella were compared to those of enrichment culture. RESULTS: Six thousand three hundred and seventy-two stool culture and PCR pairs from 5619 patients were analysed. The prevalence of salmonella was found to be 1.2 %. The sensitivity, specificity, positive predictive value and negative predictive value of PCR versus culture were 89 % (67/75), 99.8 % (6286/6297), 86 % (67/78) and 99.9 % (6286/6294), respectively. CONCLUSION: Enrichment culture is significantly more sensitive than PCR using the BD MAX Enteric Bacterial Panel for detecting salmonella in stool. Where PCR testing is used for the detection of enteric pathogens, we recommend that enrichment culture for salmonella be continued in parallel, unless the PCR method is shown to be at least as sensitive as culture.

Risk factors for mediastinitis following cardiac surgery: the importance of managing obesity.

BACKGROUND: Mediastinitis is a devastating complication of cardiac surgery. Previous studies have often observed small populations, been retrospective in design, and used a variety of definitions for mediastinitis. AIM: To identify risk factors for mediastinitis, and strategies to minimize its incidence. METHODS: A prospective cohort study of 4883 adult patients who underwent cardiac surgery between October 2003 and February 2009, comparing pre- and peri-operative risk factors, microbial aetiology, requirement for re-admission, length of stay and mortality between patients with and without mediastinitis. FINDINGS: Ninety (1.8%) patients were diagnosed with mediastinitis. Microbial aetiology was defined for 75 patients. Staphlyocococcus aureus was the most common isolate (30 episodes; 15 due to meticillin-resistant S. aureus). Univariate analysis revealed the following pre-operative factors associated with mediastinitis: age; body mass index; diabetes; modified logistic European System for Cardiac Operative Risk Evaluation score; urgent admission; and longer pre-operative stay (P < 0.05). Associated peri-operative factors were: combined coronary artery bypass grafting plus aortic valve replacement; longer aortic cross-clamp time; and longer cardiopulmonary bypass time (P < 0.005). Multi-variate analysis revealed that higher body mass index, combined coronary artery bypass grafting plus aortic valve replacement, and older age were associated with mediastinitis (P < 0.05). Mediastinitis was associated with re-admission to hospital, longer inpatient stay and reduced long-term survival (P < 0.05). CONCLUSION: Mediastinitis is associated with worse short-term outcomes (re-admission, length of stay) and reduced long-term survival. Obesity is the only modifiable pre-operative risk factor for mediastinitis. It may be possible to reduce risk through pre-operative weight loss programmes before elective surgery.

Microbiology and visual outcomes of culture-positive bacterial endophthalmitis in Oxford, UK.

PURPOSE: To review the microbiology of culture-positive cases of bacterial endophthalmitis, and to correlate this with visual outcomes. METHOD: Case notes were reviewed for culture-positive cases of bacterial endophthalmitis over a period from November 1999 to June 2012. Cases were identified retrospectively using a local database. The Fisher exact test was used for statistical analysis. RESULTS: Of the 47 cases of culture-positive bacterial endophthalmitis identified, 81 % occurred postoperatively, 11 % followed intravitreal injection, 6 % had an endogenous source and 2 % followed ocular trauma. Eighty-seven percent of bacteria cultured were Gram-positive. The most commonly identified organisms were coagulase-negative Staphylococci (47 %) and Streptococcus spp. (30 %). Patients were treated with intravitreal vancomycin and either amikacin or ceftazidime. All Gram-negative isolates were sensitive to aminoglycosides and ceftazidime, and all Gram-positive isolates were vancomycin-sensitive. Final visual acuity (VA) was 6/12 or better in 41 % of cases and counting fingers (CF) or worse in 30 %. Endophthalmitis caused by Streptococcus spp. was associated with a poorer final VA (OR for CF or worse = 14.9, P < 0.01). Cases caused by coagulase-negative Staphylococci had a better visual outcome (OR for VA of 6/12 or better = 5.7, P = 0.013). Five eyes were eviscerated or enucleated. Infection with Haemophilus influenzae was strongly associated with this outcome (OR = 57, P < 0.01). CONCLUSION: Over the time period of this study there was no evidence of emerging resistance to empirical antibiotics which are commonly used for the treatment of bacterial endophthalmitis. Infection with coagulase-negative Staphylococci was associated with a good visual outcome, whilst infection with Streptococcus spp. or Haemophilus influenzae was associated with a poor visual outcome.

Cost savings and clinical acceptability of an intravascular line tip culture triage policy.

BACKGROUND: Culture of intravascular line tips is useful for the diagnosis of intravascular line-related phlebitis and bacteraemia. However, the test lacks specificity, with a low predictive value for intravascular line bacteraemia. A recent randomised study showed that predictive value could be increased and costs reduced by refrigerating intravascular lines and retrieving them for culture only if there was a bacteraemia in the seven days before or after the intravascular line was received. AIM: We studied whether a similar triage policy could be introduced into our 1400-bed National Health Service (NHS) teaching hospital in the UK. We assessed cost reduction in the laboratory and clinical acceptability. METHODS: Data regarding the number of intravascular lines received, stored and cultured and blood cultures received was retrieved from the microbiology computer, for five-month periods before and after the introduction of the new triage policy. FINDINGS: Of the 134 intravascular line tips received in the five months after the policy had been introduced, 101 (75%) were stored without retrieval and 33 were cultured. Of these, 7/134 (5%) were culture positive and three matched a concurrent blood culture. Audit showed that compliance with the policy was >98%. The estimated annual cost reduction following the introduction of the policy was £3,166.96. The policy was acceptable to clinicians. CONCLUSIONS: The policy was both cost saving and clinically acceptable. If the policy were adopted throughout the NHS in the UK, the annual cost saving to the service might be in the order of £300,000.

Microbiological diagnosis of prosthetic joint infections: a prospective evaluation of four bacterial culture media in the routine laboratory.

The diagnosis of prosthetic joint infection (PJI) in the routine microbiology laboratory is labour-intensive, but semi-automated methods may be appropriate. We prospectively compared four microbiological culture methods on samples taken at prosthetic joint revision surgery. Automated BACTEC blood culture bottles and cooked meat enrichment broth were the most sensitive methods (87% and 83%, respectively, as compared with fastidious anaerobic broth (57%) and direct plates (39%)); all were highly specific (97-100%). To our knowledge, this is the first prospective study aimed at comparing culture methods in routine use in UK clinical laboratories for the diagnosis of PJI.

Impact of a clonal outbreak of extended-spectrum ß-lactamase-producing Klebsiella pneumoniae in the development and evolution of bloodstream infections by K. pneumoniae and Escherichia coli: an 11 year experience in Oxfordshire, UK.

OBJECTIVES: The objectives of this study were: (i) to describe an outbreak of multidrug-resistant Klebsiella pneumoniae in our population; (ii) to identify the potential source of this outbreak by examining antibiotic resistance trends in urocultures; (iii) to evaluate the contribution of this outbreak to resistance patterns over time in the two commonest Gram-negative blood culture isolates, namely K. pneumoniae and Escherichia coli; and (iv) to assess risk factors for multidrug resistance and the impact of this resistance on mortality and length of stay. METHODS: We searched Microbiology and Patient Administration Service databases retrospectively and describe resistance trends in E. coli and K. pneumoniae bloodstream infections (BSIs) in Oxfordshire, UK, over an 11 year period. RESULTS: An outbreak of a multidrug-resistant, CTX-M-15 extended-spectrum ß-lactamase (ESBL)-producing K. pneumoniae clone was identified and shown by multilocus sequence typing to belong to a novel sequence type designated ST490. This was associated with a sporadic change in resistance rates in K. pneumoniae BSIs with rates of multidrug resistance (defined as resistance to three or more antibiotic classes) reaching 40%. A case-control study showed prior antibiotic exposure as a risk factor for infection with this organism. During the same time period, rates of ESBL-producing Klebsiella spp. isolated from urocultures increased from 0.5% to almost 6%. By contrast, the rate of multidrug resistance in E. coli rose more steadily from 0% in 2000 to 10% in 2010. CONCLUSIONS: Changes in resistance rates may be associated with outbreaks of resistant clones in K. pneumoniae. Changing resistance patterns may affect important health economic issues such as length of stay.

In vitro antibiotic susceptibility patterns of bacterial keratitis isolates in Oxford, UK: a 10-year review.

PURPOSE: To analyse the spectrum of bacterial keratitis isolates and their in vitro antibiotic susceptibilities over a 10-year period in Oxford, UK; and to compare the in vitro efficacy of ciprofloxacin with that of the combination of gentamicin and cefuroxime over the same period. METHODS: All culture-positive corneal scrapes received from the Oxford Eye Hospital between July 1999 and June 2009 were identified retrospectively using a local microbiology database. For analysis of trends over time, the data was split into two equal 5-year periods. Statistical analysis was done using the χ² and Fisher exact tests. RESULTS: Over the 10-year study period, 467 corneal scrapes were performed of which 252 (54.0%) had positive bacterial cultures, growing a total of 267 organisms. The most commonly isolated bacteria were Staphylococci(40.1%) followed by Pseudomonasspecies (28.5%), other Gram-negative species (17.2%), Streptococci(7.1%), and Corynebacteria(6.0%). Between the first and second time periods there was an increase in the number of coagulase-negative Staphylococciand an increased resistance of the non-Pseudomonas Gram-negative group to chloramphenicol. Of the 189 isolates tested for sensitivity to both empirical antibiotic regimens, 176 (93.2%) were susceptible to ciprofloxacin whereas 188 (99.5%) were susceptible to either gentamicin or cefuroxime (P=0.0015). CONCLUSIONS: The spectrum of bacterial keratitis isolates and their in vitro antibiotic sensitivity patterns have generally remained stable over time. The combination of gentamicin and cefuroxime provides a broader spectrum of antimicrobial cover than ciprofloxacin monotherapy in Oxford, although both regimens continue to be appropriate choices for the initial management of this condition.

Streptococcus equi subspecies zooepidemicus meningitis--a case report and review of the literature.

A case is described of a 79-year-old man, trampled by his horses, who subsequently developed a wound infection and, later, meningitis. Streptococcus equi subsp. zooepidemicus was isolated as the causative organism. S. equi subsp. zooepidemicus, which carries the Lancefield Group C antigen, is an uncommon human pathogen but is commonly isolated from bacterial infections in animals, particularly horses. It is most commonly acquired by humans following animal contact. A review of the literature identified 20 previously described cases of S. equi subsp. zooepidemicus meningitis. Crude mortality following infection was 24%. All of the patients who died were over 70 years of age and the ingestion of unpasteurised dairy products was associated with all but one of the fatal cases. Hearing loss was a frequent complication, occurring in 19% of cases. Only 38% of patients made a complete recovery. Treatment regimes commonly included benzylpenicillin or a third-generation cephalosporin, with a mean treatment duration in survivors of 23 days.

Urban trench fever presenting as culture-negative endocarditis.

A young Russian man presented with increasing shortness of breath and signs of worsening aortic regurgitation. A diagnosis of infective endocarditis was made before emergency valve replacement. The infective cause was not discovered by routine culture but was suggested by electron microscopy and confirmed by serology and PCR testing.

Safety and cost savings of an improved three-day rule for stool culture in hospitalised children and adults.

Stools sent for culture from patients after three days of hospitalisation have a low yield (<1%) for bacterial enteric pathogens (BEP), excluding Clostridium difficile, and are expensive to process. A 'three-day rule' for rejection of specimens has previously been validated in adults. We evaluated a three-day rule for paediatric stool samples by retrospective review of all stool culture results from 1995 to 2002. Excluding C. difficile, yield for BEP in samples sent within three days following admission was 97/3751 (2.59%) compared with 3/1511 (0.2%) in samples sent more than three days after admission. The criteria for culture would have been met if the rule had been applied for these three samples. We prospectively evaluated potential savings if the rule were applied for both children and adults over a two-month period in 2000. Savings were greater for adults than for children. Of 490 stools from children, 38 (7.8%) samples did not meet the criteria for culture and of 206 stools from adult patients, 64 (31%) did not meet the criteria for culture. We implemented the rule between 1 March 2003 and 31 March 2006. A total of 14 439 stool samples were received from inpatients requesting culture for BEP, excluding C. difficile. Of these, 5744 (39.8%) were rejected because the criteria for culture were not met. This was estimated as an annual saving of 11,848 pounds to the Trust laboratory. If extrapolated to all NHS Trusts, the potential savings could be in the order of 1.18 million pounds annually.

Prevalence of MRSA in emergency and elective patients admitted to a vascular surgical unit: implications for antibiotic prophylaxis.

MATERIALS AND METHODS: 200 consecutive emergency/transfer and 150 consecutive elective patients admitted between April 2004 and January 2005, were studied. Data was obtained from departmental Morbidity and Mortality records and the computerised laboratory medicine information system. RESULTS: 261 (75%) of the 350 patients were screened for MRSA on admission (target 100%). The proportions of emergency/transfer and elective patients screened were similar (78% and 72% respectively). The prevalence of MRSA carriage detected by admission screening in emergency/transfer patients 30/153 (20%), was significantly higher (p<0.0001) than in elective patients 2/108 (2%). A simple decision analysis model suggests that gentamicin should be used when the prevalence of MRSA reaches 10% and vancomycin when the prevalence reaches 50%. CONCLUSIONS: The high prevalence of MRSA colonisation in emergency/transfer patients has important implications for pre-operative antibiotic prophylaxis.

Candida prosthetic valve endocarditis cured by caspofungin therapy without valve replacement.

A 64-year-old woman with a mechanical mitral valve prosthesis developed late-onset Candida endocarditis. Blood cultures grew Candida glabrata and Candida krusei. Transesophageal echocardiography demonstrated vegetations on the valve. The patient was not medically fit for valve replacement, but her condition was successfully treated with 6 weeks of intravenous caspofungin therapy.

Bacteraemia prediction in emergency medical admissions: role of C reactive protein.

AIM: To define the contribution made by C reactive protein (CRP) measurement to bacteraemia prediction in adults with medical emergencies in the UK. METHODS: This two year cohort study involved 6234 patients admitted as emergency cases to the acute medical or infectious diseases services of the Oxford Radcliffe Hospitals, in whom blood cultures were taken on arrival. The main outcome measures were bacteraemia risk associated with admission CRP concentrations, lymphocyte counts, and neutrophil counts. RESULTS: The quantitative associations between CRP concentration, admission lymphocyte count, and neutrophil count were defined. Risk of bacteraemia rose continuously as the CRP increased: no "cutoff" value was evident. Models examining combinations of CRP, neutrophil count, and lymphocyte count were developed and validated using a split sample technique. CRP contributed to a model including lymphocyte and neutrophil counts, but its effect was small. CRP alone performed no better than either a model combining lymphopenia and neutrophilia, or than lymphopenia alone. CONCLUSIONS: In patients with acute medical emergencies who are suspected of bacteraemia clinically, CRP concentrations, although associated with bacteraemia, have a limited role in bacteraemia prediction.