The safe use of metformin in heart failure patients both with and without T2DM: a cross-sectional and longitudinal study

AIMS

This study investigated the safe use of metformin in patients with (1) type 2 diabetes mellitus (T2DM) and heart failure on metformin, and (2) heart failure without T2DM and metformin naïve.

METHODS

Two prospective studies on heart failure patients were undertaken. The first was a cross-sectional study with two patient cohorts, one with T2DM on metformin (n=44) and one without T2DM metformin naive (n=47). The second was a 12-week interventional study of patients without T2DM (n=27) where metformin (500 mg immediate release, twice daily) was prescribed. Plasma metformin and lactate concentrations were monitored. Individual pharmacokinetics were compared between cohorts. Univariable and multivariable analysis analysed the effects of variables on plasma lactate concentrations.

RESULTS

Plasma metformin and lactate concentrations mostly (99.9%) remained below safety thresholds (5 mg/L and 5 mmol/L, respectively). Metformin concentration had no significant relationship with lactic acidosis safety markers. In the interventional study, New York Heart Association (NYHA) II (p<0.03) and III (p<0.001) grading was associated with higher plasma lactate concentrations, whereas male sex was associated with 47% higher plasma lactate concentrations (p<0.05). The pharmacokinetics of heart failure patients with and without T2DM were similar.

CONCLUSIONS

We observed no unsafe plasma lactate concentrations in patients with heart failure treated with metformin. Metformin exposure did not influence plasma lactate concentrations; however, NYHA class and sex did. The pharmacokinetics of metformin in heart failure patients are similar irrespective of T2DM. These findings may support the safe use of metformin in heart failure patients with and without T2DM.

Normothermic ex vivo perfusion provides superior organ preservation and enables viability assessment of hearts from DCD donors

The shortage of donors in cardiac transplantation may be alleviated by the use of allografts from donation after circulatory death (DCD) donors. We have previously shown that hearts exposed to 30 min warm ischemic time and then flushed with Celsior supplemented with agents that activate ischemic postconditioning pathways, show complete recovery on a blood-perfused ex vivo working heart apparatus. In this study, these findings were assessed in a porcine orthotopic heart transplant model. DCD hearts were preserved with either normothermic ex vivo perfusion (NEVP) using a clinically approved device, or with standard cold storage (CS) for 4 h. Orthotopic transplantation into recipient animals was subsequently undertaken. Five of six hearts preserved with NEVP demonstrated favorable lactate profiles during NEVP and all five could be weaned off cardiopulmonary bypass posttransplant, compared with 0 of 3 hearts preserved with CS (p < 0.05, Fisher's exact test). In conclusion, DCD hearts flushed with supplemented Celsior solution and preserved with NEVP display viability before and after transplantation. Viability studies of human DCD hearts using NEVP are warranted.

Increasing the tolerance of DCD hearts to warm ischemia by pharmacological postconditioning

Donation after circulatory death (DCD) offers a potential additional source of cardiac allografts. We used a porcine asphyxia model to evaluate viability of DCD hearts subjected to warm ischemic times (WIT) of 20–40 min prior to flushing with Celsior (C) solution. We then assessed potential benefits of supplementing C with erythropoietin, glyceryl trinitrate and zoniporide (Cs), a combination that we have shown previously to activate ischemic postconditioning pathways. Hearts flushed with C/Cs were assessed for functional, biochemical and metabolic recovery on an ex vivo working heart apparatus. Hearts exposed to 20-min WIT showed full recovery of functional and metabolic profiles compared with control hearts (no WIT). Hearts subjected to 30- or 40-min WIT prior to C solution showed partial and no recovery, respectively. Hearts exposed to 30-min WIT and Cs solution displayed complete recovery, while hearts exposed to 40-min WIT and Cs solution demonstrated partial recovery. We conclude that DCD hearts flushed with C solution demonstrate complete recovery up to 20-min WIT after which there is rapid loss of viability. Cs extends the limit of WIT tolerability to 30 min. DCD hearts with ≤30-min WIT may be suitable for transplantation and warrant assessment in a transplant model.

Methicillin-resistant Staphylococcus aureus control at the National University Hospital, Singapore: a historical perspective

INTRODUCTION

The National University Hospital (NUH) was the first restructured public hospital in Singapore. As the most recently established hospital in Singapore, it has a unique record of alert organisms including methicillin-resistant Staphylococcus aureus (MRSA).

MATERIALS AND METHODS

We performed a critical review of multiple data sources including surveillance reports, task force reports, published abstracts and manuscripts concerning MRSA in NUH.

RESULTS

Three themes emerged: 1) the MRSA rates have remained relatively stable through the life of the hospital despite the increased complexity of patients and intermittent intensified control efforts; 2) the major MRSA task forces were driven by surgeons and 3) a scientific approach to epidemiology has a critical role in understanding and planning interventions.

CONCLUSION

Although containment of MRSA can be accomplished to a certain degree through mobilisation of existing resources, higher goals such as eradication would require massive infusions of infrastructural, scientific and human resources to have a chance of success.

Antimicrobial susceptibility of Shigella isolates in eight Asian countries, 2001-2004

BACKGROUND AND PURPOSE

Shigellosis is a major health problem in developing countries, causing 91 million episodes and 414,000 deaths in Asia annually. Because of increasing trends towards drug resistance, this study was undertaken to monitor local resistance patterns of Shigella isolates from 8 Asian countries.

METHODS

Ninety eight Shigella isolates collected from 8 centers in 8 Asian countries from July 2001 to July 2004 were analyzed in terms of serogroup distribution and antimicrobial susceptibility.

RESULTS

The most common serogroup of Shigella isolates was Shigella flexneri (49/98, 50%), followed by Shigella sonnei (44/98, 45%). The highest resistance rate was found for trimethoprim-sulfamethoxazole (81%), followed by tetracycline (74%) and ampicillin (53%). Overall, 76 Shigella isolates (78%) were multidrug-resistant strains; S. flexneri had a higher multidrug resistance rate than S. sonnei (74% vs 23%). Increasing ciprofloxacin and ceftriaxone resistance was observed; approximately 10% and 5% of isolates were resistant to ciprofloxacin and ceftriaxone, respectively. Five ceftriaxone-non-susceptible strains (from Taiwan [3], Hong Kong [1] and The Philippines [1]) and 10 ciprofloxacin-non-susceptible strains (from Hong Kong [2], The Philippines [1], Korea [2], Vietnam [4] and Sri Lanka [1]) were isolated.

CONCLUSIONS

High rates of multidrug resistance and steady increases in ceftriaxone and ciprofloxacin resistance of Shigella are serious pubic health concerns in Asian countries. Continuous monitoring of resistance patterns among Shigella isolates is necessary.

Screening for Vancomycin-resistant Enterococci Using Stools Sent for Clostridium difficile Cytotoxin Assay is Effective: Results of a Survey of 300 Patients in a Large Singapore Teaching Hospital

Introduction: To assess the efficacy of screening stools sent for Clostridium difficile cytotoxin assay (CDTA) for surveillance of vancomycin-resistant enterococci (VRE). Materials and Methods: From April to May 2005, all stools submitted for CDTA were also cultured for VRE using vancomycin containing culture media. Isolates were identified to species level and vancomycin resistance confirmed, followed by polymerase chain reaction (PCR) for detection of vancomycin resistance genes and DNA fingerprinting. Over 2 consecutive days during that period, stool specimens or rectal swabs were also obtained from all patients in high-risk units (haematology, oncology, renal and intensive care). Fifty-one patients in each group were compared in terms of VRE risk factors previously identified. Results and Discussion: The prevalence of VRE in both groups was similar [3/204 (1.5%) in the CDTA arm and 1/97 (1.0%) in the high-risk arm; P = 1.0, Fisher’s exact test]. Prevalence of risk factors for VRE colonisation, including age, duration of hospitalisation, exposure to antibiotics, exposure to surgical procedures, presence of malignancy and diabetes mellitus was similar in both groups (P > 0.05). Only renal failure (P < 0.05) was more common in the high-risk group. All 4 isolates of VRE identified were genetically distinct by variable number tandem repeat (VNTR) typing; 3 were Enterococcus faecium (2 with the vanB gene, 1 with vanA) and one E. faecalis. Conclusion: Less than 2% of our high-risk patients are VRE carriers. In-hospital VRE screening using stools sent for CDTA is a simple, reasonable surrogate for screening individual high-risk patients as the patient risk profile is similar and the yield comparable in a low-prevalence setting. Key words: Antibiotic resistance, Surveillance, Vancomycin-resistant enterococci

Screening for vancomycin-resistant enterococci using stools sent for Clostridium difficile cytotoxin assay is effective: results of a survey of 300 Patients in a large Singapore Teaching Hospital

INTRODUCTION

To assess the efficacy of screening stools sent for Clostridium difficile cytotoxin assay (CDTA) for surveillance of vancomycin-resistant enterococci (VRE).

MATERIALS AND METHODS

From April to May 2005, all stools submitted for CDTA were also cultured for VRE using vancomycin containing culture media. Isolates were identified to species level and vancomycin resistance confirmed, followed by polymerase chain reaction (PCR) for detection of vancomycin resistance genes and DNA fingerprinting. Over 2 consecutive days during that period, stool specimens or rectal swabs were also obtained from all patients in high-risk units (haematology, oncology, renal and intensive care). Fifty-one patients in each group were compared in terms of VRE risk factors previously identified.

RESULTS AND DISCUSSION

The prevalence of VRE in both groups was similar [3/204 (1.5%) in the CDTA arm and 1/97 (1.0%) in the high-risk arm; P = 1.0, Fisher's exact test]. Prevalence of risk factors for VRE colonisation, including age, duration of hospitalisation, exposure to antibiotics, exposure to surgical procedures, presence of malignancy and diabetes mellitus was similar in both groups (P > 0.05). Only renal failure (P < 0.05) was more common in the high-risk group. All 4 isolates of VRE identified were genetically distinct by variable number tandem repeat (VNTR) typing; 3 were Enterococcus faecium (2 with the vanB gene, 1 with vanA) and one E. faecalis.

CONCLUSION

Less than 2% of our high-risk patients are VRE carriers. In-hospital VRE screening using stools sent for CDTA is a simple, reasonable surrogate for screening individual high-risk patients as the patient risk profile is similar and the yield comparable in a low-prevalence setting.

Predominance of Candida tropicalis bloodstream infections in a Singapore teaching hospital

An 18-month epidemiologic investigation of Candida bloodstream infections in a Singapore hospital identified 52 candidemic patients: 36% of whose infections were caused by C. tropicalis, 29% were due to C. albicans, 10% with C. parapsilosis and 21% involved C. glabrata. A predominant clonal C. tropicalis strain was demonstrated. No association with ICU stay, prior exposure to fluconazole/broad-spectrum antibiotics or increased mortality was found in this apparent shift towards non-C. albicans Candida species as the primary agents of candidemia.

Inhibition of gene expression and growth by antisense peptide nucleic acids in a multiresistant beta-lactamase-producing Klebsiella pneumoniae strain

Klebsiella pneumoniae causes common and severe hospital- and community-acquired infections with a high incidence of multidrug resistance. The emergence and spread of beta-lactamase-producing K. pneumoniae strains highlight the need to develop new therapeutic strategies. In this study, we developed antisense peptide nucleic acids (PNAs) conjugated to the (KFF)(3)K peptide and investigated whether they could mediate gene-specific antisense effects in K. pneumoniae. No outer membrane permeabilization was observed with antisense PNAs when used alone. Antisense peptide-PNAs targeted at two essential genes, gyrA and ompA, were found to be growth inhibitory at concentrations of 20 muM and 40 muM, respectively. Mismatched antisense peptide-PNAs with sequence variations of the gyrA and ompA genes when used as controls were not growth inhibitory. Bactericidal effects exerted by peptide-anti-gyrA PNA and peptide-anti-ompA PNA on cells were observed within 6 h of treatment. The antisense peptide-PNAs specifically inhibited expression of DNA gyrase subunit A and OmpA from the respective targeted genes in a dose-dependent manner. Both antisense peptide-PNAs cured IMR90 cell cultures that were infected with K. pneumoniae (10(4) CFU) in a dose-dependent manner without any noticeable toxicity to the human cells.

Specific detection of enterovirus 71 directly from clinical specimens using real-time RT-PCR hybridization probe assay

Enterovirus 71 (EV71) is one of the main causative agents of hand, foot and mouth disease (HFMD) in young children. Infections caused by EV71 could lead to many complications, ranging from brainstem encephalitis to pulmonary oedema, resulting in high mortality. Thus, rapid detection of the virus is required to enable measures to be implemented in preventing widespread transmission. Based on primers and probes targeting at the VP1 region, a real-time reverse-transcriptase polymerase chain reaction (RT-PCR) hybridization probe assay was developed for specific detection of EV71 from clinical specimens. Quantitative analysis showed that the assay was able to detect as low as 5 EV71 viral copies and EV71 was detected from 46 of the 55 clinical specimens obtained from pediatric patients suffering from HFMD during the period from 2000 to 2003 in Singapore. This study showed that the single tube real-time RT-PCR assay developed in this study can be applied as a rapid and sensitive method for specific detection of EV71 directly from clinical specimens.

Identification of vaccine candidate antigens of an ESBL producingKlebsiella pneumoniae clinical strain by immunoproteome analysis

Klebsiella pneumoniae is an opportunistic pathogen which causes pneumoniae, urinary tract infections and septicemia in immunocompromised patients. Hospital outbreaks of multidrug-resistant K. pneumoniae, especially those in neonatal wards, are often caused by strains producing the extended-spectrum-beta-lactamases (ESBLs). An immunoproteome based approach was developed to identify candidate antigens of K. pneumoniae for vaccine development. Sera from patients with acute K. pneumoniae infections (n = 55) and a control group of sera from healthy individuals (n = 15) were analyzed for reactivity by Western blot against ESBL K. pneumoniae outer membrane proteins separated by 2-DE. Twenty highly immunogenic protein spots were identified by immunoproteomic analysis. The immunogenic proteins that are most frequently recognized by positive K. pneumoniae sera were OmpA, OmpK36, FepA, OmpK17, OmpW, Colicin I receptor protein and three novel proteins. Two of the vaccine candidate genes, OmpA (Struve et al. Microbiology 2003, 149, 167-176) and FepA (Lai, Y. C. et al.. Infect Immun 2001, 69, 7140-7145), have recently been shown to be essential in colonization and infection in an in vivo mouse model. Hence, these two immunogenic proteins could serve as potential vaccine candidates.

Direct identification of Pseudomonas aeruginosa from blood culture bottles by PCR-enzyme linked immunosorbent assay using oprI gene specific primers

A PCR-enzyme-linked immunosorbent assay (PCR-ELISA) was developed for direct identification of Pseudomonas aeruginosa from positive BACTEC blood culture bottles. PCR primers were designed to target a 249 bp sequence of the oprI gene in P. aeruginosa. Biotin-labeled probe (PA3) targeted to the species-specific motif were hybridized to the digoxigenin-labeled amplified products from P. aeruginosa and captured on streptavidin-coated microtiter plates. The specificity of the assay using the PA3 probe was investigated with a range of microorganisms, which are commonly isolated from blood culture bottles serving as negative controls. The PCR-ELISA assay was shown to be highly specific for the identification of P. aeruginosa and was 10-fold more sensitive than an agarose gel-based detection method using the same pair of primers, with a detection limit at 10 fg of template. The PCR-ELISA assay developed in this study is 100% sensitive and 100% specific as it correctly identified all 73 positive and 42 negative controls as well as 25 double blind clinical samples. It significantly reduces the time needed for the identification of P. aeruginosa from positive BACTEC blood cultures bottles from 2-3 days to 6-8h.

Rapid detection of codon 460 mutations in the UL97 gene of ganciclovir-resistant cytomegalovirus clinical isolates by real-time PCR using molecular beacons

A rapid real-time polymerase chain reaction (PCR) assay using molecular beacons has been developed for the simultaneous detection of wild-type and mutant strains of cytomegaloviruses (CMV) with respect to codon 460 of the UL97 gene has been developed. The molecular beacons were designed to complement the wild-type codon 460 or the mutant sequence arising from a single base-pair difference (point mutation). Discrimination between wild-type and mutant templates was demonstrated as the beacons did not generate fluorescence with their respective mismatch targets but only with those that they were designed to perfectly anneal with. Samples that harbor mixed populations of CMV could also be readily recognized. Applied to a small number of clinical samples, the retrospective screening by this assay are in general concordance with that obtained by PCR-RFLP. Using molecular beacons strategy, codon 460 mutation was detected in ten out o the total number of 40 samples, whereas the latter method identified nine samples as containing the mutation. The discrepant result arose from the genotyping of one clinical sample as mixed (containing both wild-type and mutant CMV strains) by molecular beacons but as wild-type by PCR-RFLP, suggesting that this real-time strategy is possibly more sensitive for mutation analysis.

High prevalence of antimicrobial resistance among clinical Streptococcus pneumoniae isolates in Asia (an ANSORP study)

A total of 685 clinical Streptococcus pneumoniae isolates from patients with pneumococcal diseases were collected from 14 centers in 11 Asian countries from January 2000 to June 2001. The in vitro susceptibilities of the isolates to 14 antimicrobial agents were determined by the broth microdilution test. Among the isolates tested, 483 (52.4%) were not susceptible to penicillin, 23% were intermediate, and 29.4% were penicillin resistant (MICs >/= 2 mg/liter). Isolates from Vietnam showed the highest prevalence of penicillin resistance (71.4%), followed by those from Korea (54.8%), Hong Kong (43.2%), and Taiwan (38.6%). The penicillin MICs at which 90% of isolates are inhibited (MIC(90)s) were 4 mg/liter among isolates from Vietnam, Hong Kong, Korea, and Taiwan. The prevalence of erythromycin resistance was also very high in Vietnam (92.1%), Taiwan (86%), Korea (80.6%), Hong Kong (76.8%), and China (73.9%). The MIC(90)s of erythromycin were >32 mg/liter among isolates from Korea, Vietnam, China, Taiwan, Singapore, Malaysia, and Hong Kong. Isolates from Hong Kong showed the highest rate of ciprofloxacin resistance (11.8%), followed by isolates from Sri Lanka (9.5%), the Philippines (9.1%), and Korea (6.5%). Multilocus sequence typing showed that the spread of the Taiwan(19F) clone and the Spain(23F) clone could be one of the major reasons for the rapid increases in antimicrobial resistance among S. pneumoniae isolates in Asia. Data from the multinational surveillance study clearly documented distinctive increases in the prevalence rates and the levels of antimicrobial resistance among S. pneumoniae isolates in many Asian countries, which are among the highest in the world published to date.

Rapid detection of Klebsiella pneumoniae from blood culture bottles by real-time PCR

A LightCycler real-time PCR hybridization probe-based assay which detects a partial Klebsiella pneumoniae 16S rRNA gene was developed for the rapid identification of K. pneumoniae directly from growth-positive blood culture bottles (BACTEC 9240 system) within 2 h. No cross-reactivity was observed with 65 negative-control blood cultures that grew bacteria other than K. pneumoniae and 48 negative blood cultures from double-blind experiments, thus demonstrating 100% specificity when compared to results of conventional biochemical characterization. The assay also showed 100% sensitivity, as it correctly identified all 142 positive-control blood cultures and 4 from double-blind trials.

Fluoroquinolone Resistance in Clinical Isolates ofStreptococcus pneumoniaefrom Asian Countries: ANSORP Study

Seventeen clinical isolates of Streptococcus pneumoniae showing reduced susceptibility to ciprofloxacin (MIC >/= 4 micro g/ml) collected from eight different Asian countries were analyzed by antimicrobial susceptibility, serotyping, pulsed-field gel electrophoresis (PFGE), and DNA sequencing of the quinolone resistance-determining regions (QRDRs) in gyrA, gyrB, parC, and parE. All isolates but one showed more than one amino acid alteration in QRDRs of four responsible genes. Ile460 --> Val in parE was the most common mutation. Data suggest that Lys137 --> Asn in parC may be a primary step in the development of high-level and multiple FQ resistance. An additional mutation of Ser81 --> Phe in gyrA resulted in high-level resistance to ciprofloxacin, levofloxacin, and gatifloxacin, whereas Ser79 --> Phe in parC may exert an important role in the development of moxifloxacin resistance. Two novel amino acid changes in gyrB, Ala390 --> Val and Asn423 --> Thr, were found. Data from PFGE suggest an introduction and local spread of multiple resistant Spain(23F)-1 clone in Hong Kong, but isolates from other Asian countries were not related to this clone.

Role of clinical judgment in the application of a nucleic acid amplification test for the rapid diagnosis of pulmonary tuberculosis

BACKGROUND

Several nucleic acid amplification (NAA) tests for Mycobacterium tuberculosis (MTB) have been licensed for the rapid diagnosis of active pulmonary tuberculosis (PTB) in respiratory secretions. There is uncertainty however regarding the practical application of these tests in clinical decision making.

OBJECTIVE

To evaluate the utility of the COBAS AMPLICOR assay (Roche Diagnostics; Singapore) for MTB as applied by specialists for the rapid diagnosis of PTB in the routine clinical setting.

DESIGN

A prospective study of consecutive patients suspected of PTB and tested with the AMPLICOR assay under the care of respiratory physicians. The final diagnosis was based on all relevant clinical information after at least 3 months of follow-up. Accuracy of the NAA test was compared with that of the initial expectant treatment. Expectant treatment was based on an integrated approach that incorporated clinical evaluation with results of direct smear and NAA tests.

RESULTS

The incidence of PTB in 168 patients was 32%. The basis for expectant treatment of PTB was positive smear result in 47%, clinical suspicion in 26%, and positive AMPLICOR result in 23%. The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of the AMPLICOR test were 77%, 100%, 99%, 90%, and 93%, respectively. In comparison, they were 96%, 97%, 94%, 98%, and 97%, respectively, for the integrated clinical approach.

CONCLUSIONS

In the rapid diagnosis of PTB, the clinical judgment of specialists augmented the utility of the NAA test: (1) specialists selected patients with high-to-moderate pretest probabilities, (2) they commenced treatment promptly on a positive NAA test result, and (3) they were willing to start treatment in some patients on the basis of high clinical suspicion despite negative smear and negative NAA test results.

Community-acquired methicillin-resistant Staphylococcus aureus infection in Singapore is usually "healthcare associated"

OBJECTIVE

To assess the frequency of community-acquired methicillin-resistant Staphylococcus aureus (MRSA) infections.

SETTING

A teaching hospital in Singapore.

METHODS

Prospectively collected surveillance data were reviewed during a 1-year period to determine the extent and origin of community-acquired MRSA infections.

RESULTS

Whereas 32% of 383 MRSA infections were detected less than 48 hours after hospital admission and would, by convention, be classified as "community acquired," all but one of these were among patients who had been exposed to outpatient centers including dialysis or chemotherapy clinics, visiting nurses, community hospitals, or all three.

CONCLUSIONS

With health care increasingly being delivered in an outpatient setting, community-acquired MRSA infections are often acquired in hospital-related sites and most may be more accurately described as "healthcare acquired." Infection control measures need to move beyond the traditional paradigm of acute care hospitals to effectively control the spread of resistant pathogens.

What is true community-acquired urinary tract infection? Comparison of pathogens identified in urine from routine outpatient specimens and from community clinics in a prospective study

In order to identify the true nature of community-acquired urinary tract infections, the uropathogens isolated from 100 patients with urinary tract infection included in a prospective study conducted in community clinics were compared to 244 isolates from outpatient urine specimens routinely submitted to the laboratory. Significant differences in both the spectrum of bacteria and their antibiograms were found between the two groups. Laboratory data analysis of uropathogens from outpatient urine specimens may not reflect the true bacteriology of urinary tract infections acquired in the community. Hence, surveys based on laboratory data alone may overestimate resistance rates, leading to misinformed choices being made when treatment is empirical.

Sequence and phylogenetic analysis of SH, G, and F genes and proteins of Human respiratory syncytial virus isolates from Singapore

To study the genetic variability and molecular epidemiology of Human respiratory syncytial virus (HRSV) occurring in Singapore, nucleotide sequencing of three membrane-associated genes (SH, G and F) of four local isolates was performed. Comparison of their nucleotide and amino acid sequences with those of the prototype strains A2 (subgroup A) and CH-18537 (subgroup B) indicated that the Singapore isolates belong to the subgroup A. Comparison of the Singapore isolates with the reference strain A2 showed that whereas the G protein was the most divergent with up to 15% difference, the F and SH proteins showed less diversity of only up to 4%. Each gene exhibited its distinct variable and conserved regions. The N- and O-glycosylation sites within the G protein of the isolates were analyzed to ascertain their potential implications on the antigenicity of the viral glycoprotein. Based on the second variable region of the G protein, phylogenetic analysis of the Singapore isolates with 91 previously identified genotypes of subgroup A revealed that more than one genotype (GA2 and GA5) may circulate in the local population at a given time. This epidemiological study reflects the pattern of genetic relationships between the HRSV isolates from Singapore to those from other parts of the world.

Adult community acquired bacterial meningitis in a Singaporean teaching hospital. A seven-year overview (1993-2000)

BACKGROUND

The objective of this study is to describe the bacteriological, clinical and laboratory features of community acquired bacterial meningitis in adults admitted to a Singapore tertiary-care hospital.

METHODS

Two hundred sixty-nine cases of meningitis or meningoencephalitis admitted between 1993 and 2000 were identified by their discharge diagnosis codes. All case records except for 57 which could not be retrieved were retrospectively reviewed. Patients less than 14 years or with skull fractures, post-neurosurgery or with indwelling intracranial devices were excluded. Inclusion criteria was a clinical picture compatible with a diagnosis of bacterial meningitis with either (1) positive cerebral-spinal fluid (CSF) cultures or latex coagglutination or CSF neutrophilic pleocytosis accompanied by positive blood cultures or (2) in the absence of positive blood cultures, CSF cultures and latex agglutination, presence of CSF pleocytosis of at least 100 neutrophils per microL.

RESULTS

Fifteen "culture-positive" and 11 "culture negative" cases were identified. Six (55%) of the "culture-negative" cases received antibiotics prior to admission. Cultures grew Streptococcus pneumoniae in four cases, three cases each of Group B streptococci and Neisseria meningitides. Listeria monocytogenes and Klebsiella pneumoniae were each seen twice and Streptococcus suis once. All cases of Group B streptococci occurred in the year 1998. Mortality was 19% (n = 5), six developed infections in other sites, three epileptic seizures, three developed hydrocephalus, and two hearing loss.

CONCLUSIONS

Pathogens are similar to those reported in other studies but for an outbreak of Group B Streptococcus in 1998. There were a high number of "culture-negative" cases which may be due to preceding antibiotic intervention.

What is the optimal approach for using a direct amplification test in the routine diagnosis of pulmonary tuberculosis? A preliminary assessment

OBJECTIVE

The aim of this study was to determine the most appropriate strategy for the rapid diagnosis of pulmonary tuberculosis (PTB) using a nucleic acid amplification (NAA) test.

METHODOLOGY

This was a prospective study of 128 adult patients in whom respiratory secretions were tested for Mycobacterium tuberculosis by the AMPLICOR assay. The basis for starting PTB treatment was noted for each patient. The optimal approach was determined by using Bayes' theorem to compare different combinations of pretest probability, smear results with the AMPLICOR test.

RESULTS

The incidence of PTB was 15.6%. In only one patient was treatment for PTB commenced because of a positive AMPLICOR result. The rest were managed according to the conventional approach which relied upon clinical judgment and direct smear. The optimal approach was to treat patients with high or intermediate pretest risk for PTB who returned positive AMPLICOR tests. The overall accuracies of the conventional approach, AMPLICOR test and optimal approach were 89.8, 95.3 and 96.1%, respectively.

CONCLUSION

This small study suggests that NAA testing be limited to patients with high or intermediate pretest risk of PTB. In this group, positive results demand treatment while the management of those with negative results still relies on clinical judgment.

The pattern of utilisation and accuracy of a commercial nucleic acid amplification test for the rapid diagnosis of Mycobacterium tuberculosis in routine clinical practice

BACKGROUND

Several nucleic acid amplification (NAA) tests are available for the rapid detection of Mycobacterium tuberculosis (MTB) in clinical specimens.

AIMS

To identify the pattern of utilisation and accuracy of the AMPLICOR test in routine clinical practice in an acute care setting.

DESIGN

A retrospective descriptive study.

METHOD

We studied 159 consecutive specimens in which the AMPLICOR (Roche; Branchburg, NJ) test was requested by attending doctors. The sensitivities and specificities of the AMPLICOR for detection of active tuberculosis (TB) were calculated in relation to types of specimens, smear and culture results.

RESULTS

The number of requests more than doubled from 1999 to 2000. Thirty-eight percent of the specimens were not from the respiratory tract. The majority of the specimens had requests for one or more additional test (mean 1.8). The rate of active TB was 18%. The sensitivities of the AMPLICOR on per specimen, per patient, per smear negative specimen and per smear negative patient basis were found to be 81%, 80%, 66.7% and 71.4% respectively. The specificities for these groups accordingly were 99%, 98.6%, 99% and 98.6% respectively. The sensitivity and specificity for respiratory specimens were 97.5% and 98.5%, while for non-respiratory specimens, they were 60% and 100%. In smear negative specimens, the sensitivity and specificity for respiratory specimens were 60% and 98.5%, while for non-respiratory specimens, they were 75% and 100%. The AMPLICOR assay was negative in all 21 specimens of pleural or spinal fluid.

CONCLUSIONS

There is a growing demand for NAA in the rapid diagnosis of TB with a high proportion of non-respiratory specimens. The number of additional diagnostic tests performed on each specimen should be limited. In routine clinical practice, the AMPLICOR assay is a useful confirmatory test for active pulmonary TB. The utility of the AMPLICOR assay for MTB detection in exudative fluid specimens needs further evaluation.

Endemic typhus in Singapore--a re-emerging infectious disease?

Singapore is a modern urban city and endemic typhus is thought to be a disease of the past. This may be due to lack of specific serological testing as indirect immunoperoxidase testing using specific rickettsial antigens (U.S. Army Medical Research Unit, Institute of Medical Research, Kuala Lumpur, Malaysia) has only recently become available. In the last fourteen months, twenty-one cases of endemic typhus were diagnosed in patients hospitalised for acute febrile illnesses at the National University Hospital. We conducted a case control study to define the clinical and laboratory features of endemic typhus in Singapore.

METHOD

Demographic, clinical and laboratory data were reviewed for cases and twenty-one age and sex matched controls who had negative serologic tests as part of a work-up for fever of unknown origin.

RESULTS

Apart from a higher initial temperature (39 degrees C vs 37.9 degrees C (p < 0.001)) and ALT(p = 0.002), cases and controls had similar presentations of fever, myalgia, headache, cough, normal WBC and platelet counts. Singapore residents and migrant workers were represented in both groups (p = ns).

CONCLUSION

Endemic typhus remains an important cause of acute febrile illness in Singaporein both the local and migrant worker populations. The presentation is similar to other causes of acute febrile illnesses and the diagnosis will be missed unless it is specifically sought.

Epidemiological, clinical and laboratory characteristics of 19 serologically confirmed rickettsial disease in Singapore

AIM

To identify epidemiological, clinical and laboratory features of serologically-proven typhus in the local setting.

METHOD & RESULTS

Retrospective study looking at rickettsial serologies done over a six-month period and collection of the epidemological, clinical, laboratory and treatment response data from the case notes of the patients with an ordered rickettsial serology. Twenty of the 35 cases had a positive serology. Of these 20 patients, 18 were already clinically diagnosed as having murine typhus. All except one were males and all were migrant workers. Majority of the patients were construction workers staying in containers where rats abound. The most consistent clinical features were high fever (100%) for a median period of seven days, headache (94%) and cough (47%). The white cell count was usually normal (74%) but thrombocytopenia was common (68%). Transaminitis was also common (90%) with the AST component higher than the ALT in half of the cases. Response to doxycycline therapy was rapid and most (88%) were afebrile by 72 hours.

CONCLUSION

Typhus (notably murine type) can be confidently diagnosed from consistent clinical features supported by epidemiological and laboratory clues. Early recognition with the prompt treatment response will result in shorter hospital stay with decreased cost. Serological testing may only prove useful in difficult situations when the clinical diagnosis is less clear.

Widespread resistance to new antimicrobials in a university hospital before clinical use

The activity of cefpirome, cefepime and piperacillin/tazobactam previously unused in the hospital was evaluated in parallel with five broad-spectrum antibiotics (ceftazidime, ceftriaxone, imipenem, ciprofloxacin and amikacin) currently being used to treat serious infections in the National University Hospital, Singapore. Two hundred and two clinically significant, organisms consecutively isolated during 1998 were included in the study. In vitro efficacy of cefepime, cefpirome and piperacillin/tazobactam was not superior to imipenem, ciprofloxacin and amikacin which are currently used. More than 40% of Enterbacteriaceae were found to be ESBL producers. The incidence of nosocomial organisms resistant to drugs used in serious infections had increased since 1995. Imipenem-resistance occurred in 34.4% of Acinetobacter spp. and 19.2% Pseudomonas aeruginosa. No single agent appeared to be suitable for empirical monotherapy of serious sepsis.

Relationship between estimated pretest probability and accuracy of automated Mycobacterium tuberculosis assay in smear-negative pulmonary tuberculosis

BACKGROUND

The AMPLICOR assay (Roche; Branchburg, NJ), a rapid direct amplification test for Mycobacterium tuberculosis, has only been licensed for use in smear-positive respiratory specimens. However, many patients with pulmonary tuberculosis (PTB) have smear-negative disease. The clinical utility of this test in patients with smear-negative PTB is unknown.

OBJECTIVE

To evaluate the effect of pretest probability of PTB estimated by chest physicians on the accuracy of the AMPLICOR assay in patients with smear-negative PTB.

DESIGN AND METHODS

A prospective study of consecutive patients suspected of having smear-negative PTB. Two chest physicians estimated the pretest probability of active disease (high, intermediate, and low categories). Respiratory specimens were examined with radiometric broth medium cultures and with the AMPLICOR assay for M tuberculosis. The decision on a final diagnosis of PTB was blinded to the AMPLICOR results.

RESULTS

Active PTB was diagnosed in 25 of 441 patients (5.7%). The AMPLICOR assay had an overall sensitivity of 44% and a specificity of 99%. Results of the assay were negative in seven patients with culture-negative PTB. The proportions of patients in the high, intermediate, and low pretest groups were 4.5%, 19.7%, and 75.7%, respectively. The incidence of PTB for each group was 95%, 3.4%, and 0.9%, respectively. The sensitivities of the AMPLICOR assay in the three groups of patients were 47%, 33%, and 33%, respectively, while the specificities were 100%, 98%, and 99%, respectively.

CONCLUSIONS

In patients suspected of having smear-negative PTB, the following conclusions were drawn: (1) the incidence of active PTB was low; (2) pretest estimates accurately discriminated between patients with high and low risk of PTB; (3) the risk of PTB was overestimated in the intermediate group; and (4) the utility of the AMPLICOR assay in the intermediate-risk group may be limited by the overestimation of disease prevalence and low test sensitivity. Further studies are needed on the role of the AMPLICOR assay in better selected patients with an intermediate risk of having smear-negative PTB.

Invasive Haemophilus influenzae type b infections in Singapore children: a hospital-based study

OBJECTIVE

A 6-year (1990-95) hospital-based retrospective study was carried out to investigate the pattern of invasive Haemophilus influenzae type b (Hib) disease.

METHODOLOGY

Cases with Hib isolated from sterile sites (blood, cerebrospinal fluid, or joint aspirate) were identified from the hospital's microbiological records, and their reviewed case records. Patients with pyogenic meningitis in the same study period were also identified to estimate the incidence of Hib meningitis.

RESULTS

Twelve patients had positive cultures from sterile sites, of whom nine children were less than 5 years of age. These included seven cases of meningitis, one patient with acute epiglottitis, and one case of pneumonia. Three of the seven patients with meningitis had significant long-term sequelae. Our data also suggests a relatively low proportion of ethnic Chinese children with invasive disease. It was estimated that 18.4% to 41.1% of pyogenic meningitis in children admitted to the National University Hospital were due to Hib. The estimated annual attack rate of invasive Hib disease was at most 3.3 per 100 000 children aged less than 5 years (95% confidence interval: 2.6-3.5/100 000).

CONCLUSION

: Invasive Hib infections are relatively uncommon in our community. This justifies the need for a cost effectiveness study before a universal Hib vaccination program is implemented.

Dissemination of respiratory secretions during tracheal tube suctioning in an intensive care unit

Most intensive care patients require frequent tracheal toilet, a procedure usually performed by suctioning the tracheal tube. Such procedures often result in the production and dissemination of droplets. We measured the distance visible droplets disseminated during tracheal tube suctioning of patients in an adult surgical intensive care unit. Fifty consecutive suction procedures in 14 patients intubated with a cuffed tracheal tube were investigated. Visible droplets were scattered over a mean distance of 60 +/- 39 cm (range 25 to 168 cm) from the tracheal tube. Blood agar culture plates were placed at three fixed points from the tracheal tube to identify organisms resulting from environmental contamination (control plates). This was repeated during suctioning procedures (study plates) to look into the occurrence of bacteriological cultures that differ from the control plates. Nine of the 14 patients had tracheal tube aspirate cultures done as part of their work-up for sepsis. In more than 30% of the suctioning procedures on these 9 patients, study plates grew bacteria that were similar to those present in their tracheal tube aspirates. In view of these observations, greater care should be taken to avoid contamination of the patient's immediate environment during tracheal tube suctioning and in the design of the intensive care unit.

Seasonal trends of viral respiratory tract infections in the tropics

To evaluate the seasonal trends of viral respiratory tract infections in a tropical environment, a retrospective survey of laboratory virus isolation, serology and immunofluorescence microscopy in two large general hospitals in Singapore between September 1990 and September 1994 was carried out. Respiratory tract viral outbreaks, particularly among infants who required hospitalization, were found to be associated mainly with respiratory syncytial (RSV) infections (72%), influenza (11%) and parainfluenza viruses (11%). Consistent seasonal variations in viral infections were observed only with RSV (March-August) and influenza A virus (peaks in June, December-January). The RSV trends were associated with higher environmental temperature, lower relative humidity and higher maximal day-to-day temperature variation. Although the influenza A outbreaks were not associated with meteorological factors, influenza B isolates were positively associated with rainfall. These data support the existence of seasonal trends of viral respiratory tract infections in the tropics.

Otitis externa--the clinical pattern in a tertiary institution in Singapore

Otitis externa is a common condition in the tropics. Most of the data related to the condition have arisen from Western sources. Locally, the aetiology and the pathogens identified have not been systematically studied. A prospective study involving 107 patients was conducted. Otomycosis was frequently encountered. Coagulase negative Staphylococcus and Aspergillus niger were the most common bacteria and fungus cultured respectively. Gentamicin and polymyxin B were the most effective topical agents against Pseudomonas aeruginosa. Self-cleaning of the ears was the most common predisposing factor.