Methicillin-resistant Staphylococcus aureus bacteraemia in Hong Kong

Bloodstream infections with emphasis on Methicillin-resistant Staphylococcus aureus at the University of Gondar Comprehensive Specialized and Referral Hospital, Northwest Ethiopia

BACKGROUND

Staphylococcus aureus is the most common cause of bloodstream infections worldwide. Methicillin-resistant S. aureus is becoming more prevalent in bacteremia and septicemia cases. Thus, this study determined Staphylococcal bacteremia, Methicillin-resistant S. aureus infections, and antimicrobial susceptibility patterns of the isolates in Northwest Ethiopia.

METHODS AND MATERIALS

This retrospective cross-sectional study was conducted on all age bloodstream suspected patients at the University of Gondar Comprehensive Specialized and Referral Hospital from January 1th 2022 to June 30th, 2022. Data were collected using a designed data extraction tool. Blood samples were collected and inoculated to a sterile Tryptic Soya Broth. Bottles with bacterial growth were subcultured to blood agar, chocolate agar, MacConkey agar, and mannitol salt agar plates. Antimicrobial susceptibility testing was performed using the Kirby Bauer disc diffusion technique. The data were entered using Epi-info version 7 and exported to SPSS version 20 for analysis.

RESULTS

Among 1200 patients included in this study, 719 (59.9%) were males. The prevalence of S. aureus and Methicillin-resistant S. aureus was 26.2% (111/424) and 68.5% (76/111), respectively. The blood culture growth rate was 35.3% (424/1200). Among the isolated organisms, Gram-positive cocci account for 217 (51.2%) and Gram-negative bacilli were 173 (41.0%). Among S. aureus isolates, 63.7% were sensitive to gentamicin and 91.9% were resistant to penicillin. A high prevalence of bacteremia was found in males (60.1%) and ward locations at the neonatal intensive care unit (57.1%). Specifically, Methicillin-resistant S. aureus was highly prevalent in males, followed by pediatric age groups, and neonatal intensive care unit, which were 59.2%, 56.6%, and 44.7%, respectively.

CONCLUSION

In this study, the prevalence of Methicillin-resistant S. aureus bacteremia was high, indicating its spread in hospital settings such as intensive care units. This requires routine detection, molecular characterization of mecA gene, and improved infection prevention at the healthcare facility.

What To Think If the Results of the National Institutes of Health Randomized Trial of Methicillin-ResistantStaphylococcus aureusand Vancomycin-ResistantEnterococcusControl Measures Are Negative (and Other Advice to Young Epidemiologists): A Review and an Au Revoir

The incidence of methicillin-resistantStaphylococcus aureus(MRSA) and vancomycin-resistantEnterococcus(VRE) infections continues to rise in National Nosocomial Infections Surveillance system hospitals, and these pathogens are reportedly causing more than 100,000 infections and many deaths each year in US healthcare facilities. This has led some to insist that control measures are now urgently needed, but several recent articles have suggested that isolation of patients does not work, is not needed, or is unsafe, or that a single cluster-randomized trial could be used to decide such matters. At least 101 studies have reported controlling MRSA infection and 38 have reported controlling VRE infection by means of active detection by surveillance culture and use of isolation for all colonized patients in healthcare settings where the pathogens are epidemic or endemic, in academic and nonacademic hospitals, and in acute care, intensive care, and long-term care settings. MRSA colonization and infection have been controlled to exceedingly low levels in multiple nations and in the state of Western Australia for decades by use of active detection and isolation. Studies suggesting problems with using such data to control MRSA colonization and infection have their own problems, which are discussed. Randomized trials are epidemiologic tools that can sometimes provide erroneous results, and they have not been considered necessary for studying isolation before it is used to control other important infections, such as tuberculosis, smallpox, and severe acute respiratory syndrome. No single epidemiologic study should be considered definitive. One should always weigh all available evidence. Infection with antibiotic-resistant pathogens such as MRSA and VRE is controllable to a low level by active detection and isolation of colonized and infected patients. Effective measures should be used to minimize the morbidity and mortality attributable to these largely preventable infections.

New epidemiology of Staphylococcus aureus infection in Asia

Not only is Asia the most populous region in the world, but inappropriate therapy, including self-medication with over-the-counter antimicrobial agents, is a common response to infectious diseases. The high antibiotic selective pressure among the overcrowded inhabitants creates an environment that is suitable for the rapid development and efficient spread of numerous multidrug-resistant pathogens. Indeed, Asia is among the regions with the highest prevalence rates of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) and community-associated methicillin-resistant S. aureus (CA-MRSA) in the world. Most hospitals in Asia are endemic for multidrug-resistant methicillin-resistant S. aureus (MRSA), with an estimated proportion from 28% (in Hong Kong and Indonesia) to >70% (in Korea) among all clinical S. aureus isolates in the early 2010s. Isolates with reduced susceptibility or a high level of resistance to glycopeptides have also been increasingly identified in the past few years. In contrast, the proportion of MRSA among community-associated S. aureus infections in Asian countries varies markedly, from <5% to >35%. Two pandemic HA-MRSA clones, namely multilocus sequence type (ST) 239 and ST5, are disseminated internationally in Asia, whereas the molecular epidemiology of CA-MRSA in Asia is characterized by clonal heterogeneity, similar to that in Europe. In this review, the epidemiology of S. aureus in both healthcare facilities and communities in Asia is addressed, with an emphasis on the prevalence, clonal structure and antibiotic resistant profiles of the MRSA strains. The novel MRSA strains from livestock animals have been considered to constitute a public health threat in western countries. The emerging livestock-associated MRSA strains in Asia are also included in this review.

A Longitudinal Analysis of Methicillin-ResistantStaphylococcus aureusin a Hong Kong Teaching Hospital

Objectives:

To review the incidence and trends of MRSA during a 12-year (1989-2000) period at a university teaching hospital and the relationship between strain distribution by antibiogram and molecular typing.

Design:

Retrospective review of laboratory-based surveillance records on MRSA isolation and characterization of strains by antimicrobial susceptibility and PFGE. A patient episode was counted at the time when MRSA was first isolated.

Setting:

A 1,350-bed university teaching hospital in Hong Kong.

Patients:

Those with clinical isolates of MRSA.

Results:

During 1989 to 2000, the hospital recorded 1,203,175 deaths and discharges (D&D) and encountered 5,707 patient episodes of new MRSA isolation. The overall incidence of patient episodes of MRSA was 0.47/100 D&D. In 1989, the incidence was 0.81/100 D&D and fell to a low of 0.33/100 D&D in 1995, but then rose to 0.50/100 D&D in 2000. Antibiogram and DNA typing identified 5 major types. PFGE type A constituted 68% (211/312) of isolates and was present throughout the 12-year period. PFGE type B constituted 13% (40/312) of isolates and was only present from 1995 to 2000. These isolates form a distinct clone and had unique antibiotic resistance profiles.

Conclusions:

The study showed the establishment of a dominant MRSA clone (PFGE type A group) in the intensive care, medical, and surgical units and the appearance of a new MRSA strain in 1995 (PFGE type B), which partly explained the rise in incidence of MRSA cases and a disproportionate rise in MRSA bacteremia from 1995 to 2000.

[Impact on morbidity and costs of methicillin-resistant Staphylococcus aureus nosocomial pneumonia in intensive care patients]

OBJECTIVES

Prevention of methicillin-resistant Staphylococcus aureus (MRSA) nosocomial infections in the intensive care units (ICU) has been recommended for several years. However, the workload and the costs of these programs are to be weighed against the benefit obtained in terms of reduction of morbidity and costs induced by the infection. The purpose of this study was to evaluate the cost and the current morbidity of the infection with MRSA in the ICU.

METHODS

In a retrospective case-control study carried out in 2004, all patients of the 6 intensive care units of a teaching hospital having developed a MRSA nosocomial infection were included. They were paired with controls on the following criteria: department, Simplified Acute Physiology Score II (SAPSII), age (+/- 5 years), type of surgery (for the surgical intensive care units). The duration of hospitalization of the paired control had to be at least equal to the time from admission to infection of the infected patient. The costs were evaluated using the following parameters: scores omega 1, 2 and 3, duration of artificial ventilation, hemodialysis, length of ICU stay, radiological procedures, surgical procedures, total antibiotic cost and other expensive drugs.

RESULTS

Twenty-one patients with MRSA infection were included. All had nosocomial pneumonia. The 21 paired patients were similar with regard to both initial criteria and sex. Hospital mortality was not different between the 2 groups (cases=8; controls=6; p=0.41), as well as median duration of hospital stay (cases=41 days; controls=43 days; p=0.9). The duration of mechanical ventilation, number of hemodialysis or hemofiltration sessions, number of radiological procedures were similar in both groups. The total omega score was not significantly different between cases (median 435; IQR: 218-579) and controls (median 281, IQR: 231-419; p=0.55). The median duration of isolation was 12 days for cases and 0 day for controls (p=0.0007). The pharmaceutical expenditure was significantly higher in cases (median: 1414euro; IQR: 795-4349), by comparison with the controls (median: 877euro, IQR: 687-2496) (p=0.049).

CONCLUSION

In the ICU having set up a policy intended to reduce the risk of MRSA nosocomial infections, MRSA pneumonia does not seem to involve major additional morbidity, as compared to a control population matched for similar severity of illness. It increases modestly the use of the medical resources.

Methicillin-resistant Staphylococcus aureus infection or colonization present at hospital admission: multivariable risk factor screening to increase efficiency of surveillance culturing

Identifying methicillin-resistant Staphylococcus aureus (MRSA) colonization or infection present at admission has become important in reducing subsequent nosocomial transmission, but the most efficient surveillance methods remain to be defined. We performed anterior nares surveillance cultures of all patients upon admission to and discharge from the general internal medicine floor in our community hospital over a 7-week period, and patients completed a questionnaire on MRSA risk factors. Of the 401 patients, 41 (10.2%) had MRSA upon admission. Of the 48 risk measures analyzed, 10 were significantly associated with admission MRSA, and 7 of these were independently associated in stepwise logistic regression analysis. Factor analysis identified eight latent variables that contained most of the predictive information in the 48 risk measures. Repeat logistic regression analysis including the latent variables revealed three independent risk measures for admission MRSA: a nursing home stay (relative risk [RR], 6.18; 95% confidence interval [95% CI], 3.56 to 10.72; P < 0.0001), prior MRSA infection (RR, 3.97; 95% CI, 1.94 to 8.12; P = 0.0002), and the third latent variable (factor 3; RR, 3.14; 95% CI, 1.56 to 6.31; P = 0.0013), representing the combined effects of homelessness, jail stay, promiscuity, intravenous drug use, and other drug use. Multivariable models had greater sensitivity at detecting admission MRSA than any single risk measure and allowed detection of 78% to 90% of admission MRSA from admission surveillance cultures on 46% to 58% of admissions. If confirmed in additional studies, multivariable questionnaire screening at admission might identify a subset of admissions for surveillance cultures that would more efficiently identify most admission MRSA.

Assessing the macroeconomic impact of a healthcare problem: the application of computable general equilibrium analysis to antimicrobial resistance

There is a positive relationship between the health of a nation and its economic prosperity. However, in evaluating health care, economists typically concentrate on the economic impact only to the health (care) sector, which may mis-specify the social costs and benefits of a disease or intervention. This paper demonstrates the value of using a macroeconomic approach to modelling a major health problem, using the context of antimicrobial resistance and the application of the computable general equilibrium technique. This approach is described in detail and its 'added value' demonstrated in the case of AMR.

A comparison of clinical features and mortality among methicillin-resistant and methicillin-sensitive strains of Staphylococcus aureus endocarditis

Our objective was to assess the clinical factors that would reliably distinguish methicillin-resistant S. aureus (MRSA) from methicillin-susceptible S. aureus (MSSA) endocarditis. A retrospective cohort study of clinical features and mortality in patients with MRSA and MSSA endocarditis between March 1986 and March 2004 was performed in a 750-bed, tertiary care teaching hospital. A total of 32 patients (10 MRSA [31.3%] vs 22 MSSA [68.7%]) were evaluated. Their mean age and sex ratio (male/female) were as follows: 30.8 +/- 16.0 vs 24.4 +/- 19.6 years old and 6/4 vs 13/9, for MRSA and MSSA infective endocarditis (IE), respectively. Univariate and multivariate analyses revealed that persistent bacteremia was significantly more prevalent in MRSA IE (OR, 10.0 [1.480- 67.552]; p, 0.018). There was a higher mortality trend for MRSA IE (50.0%) than for MSSA IE (9.1%) (p=0.019). However, persistent bacteremia was not associated with higher mortality (p > 0.05). These results indicate that if persistent bacteremia is documented, the likelihood of MRSA endocarditis should be viewed as high, and the patient's anti- staphylococcal therapy should be prolonged and/or changed to a more "potent" regimen.

Characterization of isolates of methicillin-resistant Staphylococcus aureus from Hong Kong by phage typing, pulsed-field gel electrophoresis, and fluorescent amplified-fragment length polymorphism analysis

The genetic relatedness of 127 methicillin-resistant Staphylococcus aureus (MRSA) isolates, belonging to five major types as identified by pulsed-field gel electrophoresis (PFGE) and antibiotic resistance profiles, was examined further using phage typing and fluorescent amplified fragment length polymorphism (FAFLP). The MRSA isolates were recovered from patients at the Prince of Wales Hospital (PWH), Hong Kong, over a 13-year period, 1988 to 2000. These strains were also compared with representatives of the well-described MRSA international clones and with epidemic MRSA strains (eMRSA) 1 to 16 from the United Kingdom. Phage typing distinguished two major "clones" at this hospital: all of the phage type 1 (PT1) isolates belonged to PFGE types A, C, D, and E, while most of the PT2 isolates were associated with PFGE type B, which exhibited a unique antibiotic resistance profile. MRSA isolates belonging to PFGE subtype A2 were indistinguishable from the British eMRSA-1, while isolates of PFGE type B were closely related to eMRSA-9 by PFGE. Based on FAFLP, all five predominant PFGE types at the PWH belonged to one group and fell into the same cluster as eMRSA-1, -4, -7, -9, and -11 isolates. Multilocus sequence typing and staphylococcal cassette chromosome mec typing classified representatives of our MRSA isolates as members of the same clone (ST239-MRSA-III). Thus, the predominant MRSA isolates frin the PWH in the last decade are closely related to early United Kingdom eMRSA clones 1, 4, and 11 and are members of a lineage that includes the Brazilian MRSA clone.

SHEA guideline for preventing nosocomial transmission of multidrug-resistant strains of Staphylococcus aureus and enterococcus

BACKGROUND

Infection control programs were created three decades ago to control antibiotic-resistant healthcare-associated infections, but there has been little evidence of control in most facilities. After long, steady increases of MRSA and VRE infections in NNIS System hospitals, the Society for Healthcare Epidemiology of America (SHEA) Board of Directors made reducing antibiotic-resistant infections a strategic SHEA goal in January 2000. After 2 more years without improvement, a SHEA task force was appointed to draft this evidence-based guideline on preventing nosocomial transmission of such pathogens, focusing on the two considered most out of control: MRSA and VRE.

METHODS

Medline searches were conducted spanning 1966 to 2002. Pertinent abstracts of unpublished studies providing sufficient data were included.

RESULTS

Frequent antibiotic therapy in healthcare settings provides a selective advantage for resistant flora, but patients with MRSA or VRE usually acquire it via spread. The CDC has long-recommended contact precautions for patients colonized or infected with such pathogens. Most facilities have required this as policy, but have not actively identified colonized patients with surveillance cultures, leaving most colonized patients undetected and unisolated. Many studies have shown control of endemic and/or epidemic MRSA and VRE infections using surveillance cultures and contact precautions, demonstrating consistency of evidence, high strength of association, reversibility, a dose gradient, and specificity for control with this approach. Adjunctive control measures are also discussed.

CONCLUSION

Active surveillance cultures are essential to identify the reservoir for spread of MRSA and VRE infections and make control possible using the CDC's long-recommended contact precautions.

Effect of delayed infection control measures on a hospital outbreak of methicillin-resistant Staphylococcus aureus

All patients positive for methicillin-resistant Staphylococcus aureus (MRSA) at the University Hospitals of Geneva, Switzerland, between 1989 and 1997 (N = 1771) were included in a cohort study to evaluate the consequences of delayed containment of a hospital-wide outbreak occurring during a 4-year absence of MRSA control measures. The effects of efforts to control both the MRSA reservoir and the number of bacteraemic patients were assessed. Intensive infection control measures were initiated in 1993 and included patient screening, on-site surveillance, contact isolation, a computerized alert system, and hospital-wide promotion of hand hygiene. An increase in the rate of new MRSA-infected or -colonized patients was observed between 1989 and 1994 (from 0.05 to 0.60 cases per 100 admissions), which subsequently decreased to 0.24 cases in 1997 (P<0.001). However, the proportion of laboratory-documented methicillin-resistant isolates among all S. aureus showed little variation in the years from 1993 onwards (range, 19-24%), reflecting the result of an increase in the number of screening cultures. The annual number of patients with MRSA bacteraemia strongly correlated with the hospital-wide prevalence of MRSA patients (R(2)= 0.60; P = 0.01) and the rate of new MRSA patients (R(2)= 0.97; P<0.001). Consequently, the attack rate of nosocomial MRSA bacteraemia served as an excellent marker for the MRSA patient reservoir. In conclusion, despite delayed implementation, infection control measures had a substantial impact on both the reservoir of MRSA patients and the attack rate of MRSA bacteraemia.

Reasons for noncompliance with infection control guidelines

Concern frequently is voiced about individuals not complying with guidelines intended to prevent spread of antibiotic-resistant pathogens from patient to patient, but institutional decisions to ignore Centers for Disease Control and Prevention guidelines recommending detection and isolation of colonized patients also have contributed greatly to the increasing rate of infections due to these pathogens. This is so because colonized patients are the main reservoir for spread, and barrier precautions prevent spread much more effectively than Standard Precautions. Providing effective leadership and changing this culture of noncompliance must begin with the infection control team believing that spread is both important and preventable.

Risk factors influencing clinical outcome in Staphylococcus aureus bacteraemia in a Turkish University Hospital

A total of 101 episodes of Staphylococcus aureus bacteraemia were evaluated for the factors influencing prognosis. The overall episode mortality rate and the mortality rate due to bacteraemia were 43.6 and 21.8%, respectively. Episodes with methicillin-resistant S. aureus (MRSA) bacteraemia had a significantly higher overall mortality rate (58.7 vs. 30.9%, P<0.01) and mortality rate due to bacteraemia (32.6 vs. 12.7%, P=0.02) when compared with episodes caused by methicillin-sensitive S. aureus (MSSA). The multivariate analysis revealed that the underlying disease, presence of infective endocarditis, septic shock and central intravascular catheter and methicillin resistance of S. aureus were the five independent risk factors associated with a higher mortality rate.

Methicillin-Resistant Staphylococcus aureus Infections

Methicillin-resistant Staphylococcus aureus (MRSA) has continued to spread and cause serious nosocomial infections. Failure to control MRSA may result in higher rates of use of glycopeptides, which may, in turn, lead to higher rates of glycopeptide resistance. Resistance to glycopeptides has recently begun to appear in S. aureus. Transfer of glycopeptide-resistance genes from enterococci to S. aureus has been documented in laboratory experiments but has not yet been found in clinical isolates. Over time, MRSA is becoming more common in various subsets of the general population. Some studies claim that many MRSA-colonized outpatients and their close contacts have had no health care contacts, but these studies have usually not considered contacts in outpatient clinics. Several other recent studies have found that all or a vast majority of patients with MRSA have had frequent contact with health care providers. Failure to wash hands and disinfect equipment between patients, which has been commonly seen in studies of health care worker compliance with infection control measures, may explain much of the continuing spread. The source of spread of antibiotic-resistant microbes can be likened to an iceberg, with clinically obvious infections representing the tip of the iceberg and most of the spread coming from clinically inapparent colonized patients who represent most of the reservoir for transmission. Surveillance cultures to identify this reservoir are important to the control of spread with effective barrier precautions. Such precautions have been shown to reduce the spread of MRSA 15.6-fold compared with standard precautions.

Clinical implications of nosocomial gram-positive bacteremia and superimposed antimicrobial resistance

The coexistence of a pathogen population with an ever-increasing resistance to many antibiotics and a patient population characterized by increasingly complex clinical problems has contributed to an increase in the bloodstream infections associated with gram-positive bacteria. This serious therapeutic challenge has already been associated with an increase in infection-related morbidity and mortality, a prolongation of hospital stays, and an escalation of healthcare costs. Vancomycin resistance, long prevalent among the enterococci, has emerged in strains of Staphylococcus aureus. Several cases of infection caused by S. aureus strains with intermediate-level resistance to vancomycin (MIC=8 microg/mL) have recently been reported. As glycopeptide resistance accelerates among the gram-positive bacteria, so does the potential for adverse clinical consequences associated with bloodstream infections caused by these pathogens. The patients least able to tolerate the effects of uncontrolled bloodstream infections are also those at the highest risk for the development of infections caused by glycopeptide-resistant pathogens. In this at-risk population, a poor outcome may be anticipated if effective antibiotic therapy is unavailable. Appropriate rationing of vancomycin and other antimicrobial agents that increase the selection of antibiotic-resistant strains of gram-positive bacteria and the rapid development of novel antimicrobial agents with reliable gram-positive activity must be immediate priorities if the threat posed by glycopeptide-resistant gram-positive pathogens is to be countered.

Neonatology in the 'Pearl of the East'

Clinicians practising in different regions of the world are often impressed at marked differences in disease patterns witnessed. The bases of most obvious differences are usually socio-economic and genetic, but culture and environment can be equally important. Documenting and assessing such differences is more than just a passing interest. Globalization has resulted in significant movement of people from one area to another. During the past decade, many young Chinese families have emigrated to Australia, Europe and North America for social and political reasons. Clinicians in these regions will need to be aware of the "Chinese disease patterns'. This overview highlights some of the more striking differences seen in neonatal medicine between the East (Hong Kong) and the West (Australia/Europe/North America). In addition to the immediate clinical relevance, it is hoped that this review can provide a background from which fruitful research ideas may emerge and to stimulate interest for trainee neonatologists who wish to seek sabbatical experience in Hong Kong.

Elimination of methicillin-resistant Staphylococcus aureus from a neonatal intensive care unit after hand washing with triclosan

Evaluating hand wash products in terms of user acceptability and effectiveness against methicillin-resistant Staphylococcus aureus (MRSA) has been part of a long-term strategy to eliminate endemic MRSA from the neonatal intensive care unit at the Royal Women's Hospital (Brisbane). Following the introduction of a new hand wash disinfectant (triclosan 1% wt/vol), new cases of MRSA colonization were monitored for 12 months. In addition, the use of antibiotics, the incidence of multi-resistant Gram-negative cultures and neonatal infections were noted. No changes were made to any procedures or protocols during the trial. All babies colonized with MRSA had been discharged from the nursery within 7 months of the introduction of triclosan and in the subsequent 9 months no new MRSA isolates had been reported. Reduction in the use of vancomycin has resulted in a cost saving of approximately $A17,000. The total number of Gram-negative isolates has not increased, although Pseudomonas aeruginosa is now reported more often. Compared with the previous 12 months, fewer antibiotics were prescribed and fewer nosocomial infections recorded (P < 0.05).

Risk factors for nosocomial bacteremia due to methicillin-resistant Staphylococcus aureus

In a prospective surveillance study (February 1990-December 1991) performed at a 1000-bed teaching hospital to identify risk factors for nosocomial methicillin-resistant Staphylococcus aureus (MRSA) bacteremia, 309 patients were found to be colonized (n = 103; 33%) or infected (n = 206; 67%) by MRSA. Sixty-three of them developed bacteremia. Compared with 114 patients who had nosocomial bacteremia caused by methicillin-sensitive Staphylococcus aureus during the same period of time, MRSA bacteremic patients had more severe underlying diseases (p < 0.01), were more often in intensive care units (p < 0.01) and had received prior antibiotic therapy more frequently (p < 0.01). To further identify risk factors for MRSA bacteremia, univariate and multivariate analyses of this series of 309 patients were performed using the occurrence of MRSA bacteremia as the dependent variable. Among 14 variables analyzed, intravascular catheterization, defined as one or more intravascular catheters in place for more than 48 h, was the only variable selected by a logistic regression model as an independent risk factor (OR = 2.7, CI = 1.1-6.6). The results of this study reinforce the concept that recent antibiotic therapy may predispose patients to MRSA infection and suggest that among patients colonized or infected by MRSA, those with intravascular catheters are at high risk of developing MRSA bacteremia.

Tuberculous pericarditis with rapid progression to constriction. Prompt diagnosis and treatment are needed

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Effects of culture media on detection of methicillin resistance in Staphylococcus aureus and coagulase negative staphylococci by disc diffusion methods

AIMS

To test 10 culture media for their ability to detect resistance and sensitivity of staphylococci to methicillin by disc diffusion.

METHODS

Fifty strains of Staphylococcus aureus and 135 strains of coagulase negative staphylococci were tested using Columbia, Diagnostic Sensitivity Test, Mueller Hinton, Sensitest and Iso-sensitest agars with and without 5% added sodium chloride. Cultures were examined after 18 and 40 hours of incubation. The diameter of the zone and its characteristics were recorded and these media were assessed for their ability to produce clear, readable zones of inhibition. Changes in the variables which determined resistance were investigated. Results were analysed allowing a zone diameter reduction of 8 mm and 10 mm compared with the control in addition to the standard 6 mm.

RESULTS

Columbia agar with added sodium chloride supported the growth of all strains, detected the highest number of resistant strains, and was the easiest to read. Resistance was detected after 18 hours in most resistant strains, but some required 40 hours of incubation. There was poor agreement, however, on this medium (63-94%) between disc diffusion and the reference MIC method for sensitive strains. Allowing a greater reduction in zone size resulted in more agreement with sensitive strains but with consequently lowered detection of resistant strains. The other media showed some growth failures and more zones that were difficult to read. More resistance was detected when incubation was prolonged to 40 hours but this was consistently less than on Columbia agar with added salt.

CONCLUSIONS

None of the media detected all of the resistant strains. Columbia agar with added salt was the most satisfactory medium in this respect, but it misidentified up to 37% of the sensitive strains as resistant. Methicillin susceptibility testing by disc diffusion testing is unreliable.

Nasal carriage of methicillin-resistant Staphylococcus aureus by hospital staff in north Jordan

The nasal carriage of methicillin-resistant Staphylococcus aureus was detected in 550 hospital staff members of four hospitals in north Jordan. Of the 109 (19.8%) individuals tested who were nasal carriers of S. aureus, only 32 (5.8%) were found to be carriers of methicillin-resistant Staphylococcus aureus. The carriers were four doctors, 23 nurses, three laboratory technicians, one maid and an administrator. It was noted that 25 (78.1%) of these carriers were in constant contact with patients in operating theatres, surgical wards or intensive care units. It was not clear whether the carriers were short- or long-term carriers, or whether they were persistent sources of methicillin-resistant Staphylococcus aureus. Decontamination of these carriers was considered among other control measures to avoid the dangerous outcome of hospital outbreaks caused by this potential pathogen.

Outbreaks of infection with methicillin-resistant Staphylococcus aureus on neonatal and burns units of a new hospital

Multiple introductions of methicillin-resistant Staphylococcus aureus (MRSA) strains occurred to a new hospital in Hong Kong. Two years of clinical microbiological surveillance of the resulting outbreaks was combined with laboratory investigation by phage and antibiogram typing, and plasmid profiling. The outbreaks on the special care baby (SCBU) and burns (BU) units were studied in detail, and colonization of staff and contamination of the environment were investigated. MRSA were spread by the hands of staff on the SCBU, where long-term colonization of dermatitis was important, but were probably transmitted on the BU by a combination of the airborne, transient hand-borne and environmental routes. Simple control measures to restrict hand-borne spread on the SCBU were highly effective, but control was not successful on the BU.

Hong Kong strains of methicillin-resistant and methicillin-sensitive Staphylococcus aureus have similar virulence

While most authorities agree that methicillin-resistant Staphylococcus aureus (MRSA) are as pathogenic as methicillin-sensitive strains (MSSA), some believe that MRSA are relatively avirulent opportunists, and that their importance has been exaggerated. We present evidence that Hong Kong strains of MRSA and MSSA are equally pathogenic: they have similar virulence in animal models; they are isolated in similar proportions from both deep and superficial clinical sites including blood; in patients with hospital-acquired bacteraemias mortality rates are similar when adjusted for clinical factors; and in both animals and patients with systemic MRSA infection, mortality rates are significantly reduced by vancomycin therapy. Efforts to control the spread of MRSA are justified, and in invasive sepsis early treatment with vancomycin may be life-saving.