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.

Fungal colonisation in digital silicone rubber prostheses

The fungal discolouration of silicone rubber prostheses is reported in four cases. In two of the cases, the discolouration was caused by the fungus Candida tropicalis. In the other two cases, two different fungal organisms, namely Trichoderma sp. and Scedosporium prolificans were incriminated. The non-porous silicone rubber layers create an enclosed environment in the suction cup of the prosthesis and preclude ventilation at the prosthesis-stump interface. The moisture as a result of sweat and body warmth in the stump assists fungal growth. Residual salts from the sweat, sebum from sebaceous glands and the residues from petroleum jelly (Vaseline) applied to facilitate donning, can adhere to the surfaces of the prosthesis and provide the nutrients for fungal growth. Prolonged continuous usages of the prosthesis, the presence of sweaty palms in the users, donning the prosthesis during manual physical activities which induce perspiration, washing of hands with the prosthesis on and warm humid climatic conditions have been identified as factors predisposing the prosthesis to fungal colonisation. The fungal growth caused a black discolouration and marred the aesthetic quality of the prostheses. As a preventative measure, daily immersion of the prostheses in denture cleaner such as benzalkonium chloride, or water at 60 degrees C for 15 minutes, or decontamination with 70% alcohol is recommended. Prior cleaning to remove organic matter before decontamination is emphasised.

Streptococcus suis infection complicated by purpura fulminans and rhabdomyolysis: case report and review

Streptococcus suis infection, an important zoonotic occupational disease in humans, is associated with meningitis, arthritis, and perceptive deafness. We report a case of severe S. suis infection in a previously healthy man who developed purpura fulminans and rhabdomyolysis, complications not previously reported with this disease.

In vitro activity of cefoperazone-sulbactam: Singapore experience

In vitro activity of commonly used antimicrobial agents against consecutively isolated 521 strains of Gram negative bacilli causing serious infections in the National University Hospital, Singapore were tested in parallel with cefoperazone-sulbactam combination. With the combination complete resistance of 2% and intermediate resistance of 5% were noted among the 521 strains tested. Resistance to imipenem was low (5%) but resistance against other antimicrobial agents varied from 12% (amikacin) to 80% (ampicillin). In vitro data demonstrated a possible future role for cefoperazone-sulbactam in the treatment of sepsis caused by Gram negative bacilli in our hospital.

Genital Group B Streptococcus carriage in the antenatal period: its role in prom and preterm labour

Of 326 high vaginal swabs taken during the antenatal period, Group B Streptococcus (GBS) was isolated from the birth canal in 46 women, giving a carrier rate of 14.1%, which is within the often quoted range of between 5% - 25% in different parts of the world. Carriage rates were similar at different gestations. In a subgroup of 34 women, 2 swabs taken at least 5 weeks apart yielded results which were discordant in over one fifth of the time. This knowledge of the natural history of GBS carriage questions the practice of treating asymptomatic carriers of GBS in the antenatal period to prevent transmission of GBS to the neonate. The group of women with positive swabs in the antenatal period did not have a significantly higher incidence of preterm labour and/or prelabour rupture of membranes (PROM) compared with the group of women with negative swabs. Routine screening of the antenatal population for GBS carrier status prior to 32 weeks gestation may not identify women at high risk of PROM or preterm labour.

Detection of Mycobacterium tuberculosis in sputum, pleural and bronchoalveolar lavage fluid using DNA amplification of the MPB 64 protein coding gene and IS6110 insertion element

Two gene sequences specific for Mycobacterium tuberculosis were evaluated for the diagnosis of pulmonary tuberculous (PTB) in pleural fluid (PF), bronchoalveolar lavage fluid (BAL) and sputum (Sp). The 240 bp sequence (nts 460-700) coding for the MPB 64 protein coding gene and the 123 bp IS6110 insertion element present in multiple copies in the mycobacterial genome were amplified using the polymerase chain reaction. Fifty-nine clinical specimens were studied. The diagnosis of PTB was confirmed by positive M. tuberculosis cultures in 14 specimens, and by the presence of characteristic histological features of granuloma and Langerhan's giant cells on pleural biopsy in 3 PF specimens through cultures for M. tuberculosis were negative. The remaining 42 specimens were obtained from patient's with non-tuberculosis pulmonary infections or malignancy, and these served as negative controls. Our results showed that the IS6110 insertion element and MPB 64 gene sequence were detected in all 14 culture positive PTB cases, although detection of the latter sequence required both DNA amplification and oligonucleotide hybridization. There was however one false positive specimen with the MPB 64 detection protocol. More importantly, both the MPB 64 sequence and IS6110 insertion element protocols were unable to detect M. tuberculosis DNA in the 3 PF samples diagnosed by histological characteristics on pleural biopsy and culture negative. We conclude that DNA amplification for M. tuberculosis-specific sequences is a useful method for rapid diagnosis of PTB in culture positive specimens. However, the false negative results with TB culture negative cases of tuberculosis pleurisy, limits its usefulness for the diagnosis of tuberculous pleurisy.

Hospital acquired infections in a Singapore Hospital: 1985-1992

A prospective survey of hospital-acquired infections (HAI) was conducted from 1985 to 1992. The survey used laboratory results to estimate incidence and alert infection control staff to a need for further action. The results were analysed with regard to the site, speciality and type of organism. The distribution by speciality of patients who had methicillin resistant Staphylococcus aureus infections was compared with the distribution of all patients with HAI. Although the surveillance was only partial, the data collected from year to year over the period of study seemed constant. The distribution of infection by type, location and bacterial cause was similar to results from other parts of the world. Notable differences were the high incidence of Acinetobacter sp., and the pattern of antimicrobial susceptibility to commonly used agents. Over half the Staphylococcus aureus isolates were methicillin resistant.

Antimicrobial resistance problem in a university hospital

In a study conducted in 1991 in the National University Hospital, Singapore, the susceptibilities of a total of 2156 recent clinical isolates were tested against 25 antimicrobial drugs. The organisms were those isolated from routine specimens received in the microbiology laboratory. About 40% Staphylococcus aureus isolations in the hospital were resistant to methicillin. A high incidence of the resistance was noted among Staphylococcus aureus and coagulase negative staphylococci to antistaphylococcal drugs. Acinetobacter sp. and Klebsiella sp. are becoming major threats with regard to antimicrobial treatment as they are multi-drug resistant. Pseudomonas aeruginosa did not show a resistance problem except to pefloxacin (74%). Ampicillin resistance of Acinetobacter sp. (93%) was reduced to 71% by ampicillin/clavulanic acid and to 7% by ampicillin/sulbactam. With regards to the urinary isolates higher rates of resistance were noticed with Pseudomonas aeruginosa to antipseudomonas drugs and for co-trimoxazole with other Gram negative organisms, compared to non-urinary isolates.

Bacteria, viruses, yeasts and protozoans associated with diarrheal disease in Singapore

Labile toxin producing enterotoxic E. coli (ETEC) were the commonest pathogen isolated from diarrheal stools of hospitalized children (21%) and adults (26%) in Singapore. Salmonellas ranked a close second in children (19%). Other bacterial pathogens were isolated from less than 5% of subjects. Blastocystis hominis was detected in 4.3% of diarrheal stools when a simple sedimentation technique was used. Cryptosporidium was not detected at all. An analysis of yeast counts in smears of diarrheal and non-diarrheal stools suggested they were etiologically associated with at least 6% of diarrhea in children and 19% in adults. Testing for rotaviruses by Latex agglutination and for adenovirus by electronmicroscopy showed an association with 6 per cent and 3 per cent diarrhea respectively. The study highlighted a need for: case control studies on ETEC and B. hominis; studies on the epidemiology of diarrhea by yeasts; establishing the true incidence of adenovirus diarrhea; studies on the prevalence and seasonality of rotavirus infection in Singapore.

Multiple antibiotic resistance in Klebsiella spp. and other Enterobacteriaceae isolated in Singapore

A common pattern of multiple antibiotic resistance has been noted in bacteria isolated from Singaporean patients. The resistance pattern includes: ampicillin, cefuroxime, ceftazidime and other third generation cephalosporins, aztreonam, gentamicin and other aminoglycosides. The bacterial species implicated are Klebsiellas and other members of the Enterobacteriaceae. Preliminary laboratory investigation with a disk-diffusion augmentation test suggests the presence of extended-spectrum beta-lactamases. A retrospective study of laboratory blood culture records shows a rising incidence of resistance in Klebsiella spp. since 1985. Antimicrobial susceptibility results suggest a high degree of co-transfer of aminoglycoside resistance. The high frequency of this type of multiple antibiotic resistance should result in greater caution in the selection of presumptive antibiotic therapy for septicaemia, in order to avoid treatment failure and further selection of resistant strains.

Antimicrobial susceptibilities of clinical isolates of Acinetobacter baumannii from Singapore

The in vitro activities of 17 antimicrobial agents alone or in combination against 70 clinical isolates of Acinetobacter baumannii from Singapore were determined by broth microdilution. The MICs of amoxicillin, ampicillin, ceftazidime, ceftriaxone, gentamicin, and piperacillin for 90% of the strains were > or = 128 micrograms/ml. Addition of sulbactam to ampicillin produced improved activity, whereas adding tazobactam to piperacillin did not. The MICs of amikacin, ciprofloxacin, and imipenem for 90% of the strains were 32, 32, and 16 micrograms/ml, respectively.

Increasing prevalence of antimicrobial resistance among organisms isolated from blood culture in a Singapore hospital

The blood culture isolates obtained over the period 1985-1990 in a general teaching hospital were reviewed to determine trends in the prevalence of resistance to antimicrobial drugs. The percentages of Staphylococcus aureus isolates resistant to methicillin increased each year. Resistance among coagulase negative staphylococci also increased in prevalence: by 1990 approximately 50% of such isolates were resistant to methicillin, erythromycin, co-trimoxazole and gentamicin, 24% were resistant to clindamycin, 20% to fucidic acid but only 0.5% to vancomycin. Isolates of Enterobacteriaceae, excluding community-acquired salmonellae, showed increasing prevalence of resistance to beta-lactams, as did Acinetobacter spp isolates to gentamicin, co-trimoxazole and ceftriaxone. The isolates of Pseudomonas aeruginosa were exceptional, having no evident increase in the prevalence of resistance during the period. The rapid increases observed in relation to the other pathogens indicate the need for an antibiotic policy based on continuous surveillance of susceptibility patterns in the hospital.

Nosocomial urinary tract infection: a microbiological study

Nosocomial urinary tract infection (UTI) is an important cause of increased morbidity and mortality in hospitalised patients. The increasing use of broad spectrum antibiotics will result in changes in the microbiological and antibiotic sensitivity pattern of pathogens isolated from nosocomial UTI. We have endeavoured to study the bacteriological pattern of nosocomial UTI and the antibiotic sensitivity patterns of the pathogens concerned. Over a period of one year, a total of 541 patients with 656 episodes of nosocomial UTI were studied. A total of 748 organisms were isolated. The two main complicating factors in nosocomial UTI were urogenital instrumentation (70.4%) and diabetes mellitus (24.2%). Klebsiella species (spp) was the predominant organism isolated (25.0%) and was significantly associated with age and diabetes mellitus. Klebsiella spp in nosocomial UTI showed an overall increase in resistance to antibiotics and multiple antibiotic resistant strains were not uncommon. Escherichia coli was isolated in 17.7% of cases. Streptococcus faecalis was isolated in 10.6% of cases and was significantly associated with instrumentation. Pseudomonas spp was isolated in 8.6% of cases and was generally sensitive to ceftazidime and amikacin. It was associated with systemic malignancies and the use of immunosuppressants.

Moraxella catarrhalis respiratory infection in adults

Moraxella catarrhalis (MC) is an upper respiratory tract commensal which may also be pathogenic. In this report we examined the clinical features, microbiology and therapeutic response in 30 consecutive adult patients with pneumonia who had MC isolated in the sputum. The mean age was 66 years with an equal sex ratio. Most patients gave a history of cigarette smoking (77%) and had underlying pulmonary diseases (73%). Dyspnea and productive cough were the most common complaints (87%). Fever was a manifestation in 60% of patients. Chest X-ray features of pneumonia were noted in 78% of patients while leucocytosis (> 11,000/mm3) was evident in 70%. While all isolates were susceptible to tetracycline, 70% were resistant to penicillin/ampicillin by in-vitro testing. Three patients died, two from their underlying illnesses and one from myocardial infarct. We believe that MC isolated in sputum cultures from symptomatic adults with underlying respiratory diseases should be treated as a pathogen. The short term prognosis is good.

Prospective study of the aetiology of adult community acquired bacterial pneumonia needing hospitalisation in Singapore

A prospective survey of 96 consecutive adult patients with community acquired pneumonia requiring hospitalisation was carried out at National University Hospital, Singapore. Causative pathogens were identified in 58% of patients. Mycobacterium tuberculosis was the most common pathogen (21%), followed by Streptococcus pneumoniae (12%), Haemophilus influenzae (5.2%), Mycoplasma pneumoniae (5.2%) and Staphylococcus aureus (4.2%). Gram-negative organisms (apart from Haemophilus influenzae) were found in 10% of pneumonia patients. More than half of the patients had pre-existing illness, the most common was diabetes mellitus (21%).