An outbreak of EMRSA 2 associated with long-term colonization of medical staff

Transmission of Staphylococcus aureus between health-care workers, the environment, and patients in an intensive care unit: a longitudinal cohort study based on whole-genome sequencing

Background

Health-care workers have been implicated in nosocomial outbreaks of Staphylococcus aureus, but the dearth of evidence from non-outbreak situations means that routine health-care worker screening and S aureus eradication are controversial. We aimed to determine how often S aureus is transmitted from health-care workers or the environment to patients in an intensive care unit (ICU) and a high-dependency unit (HDU) where standard infection control measures were in place.

Methods

In this longitudinal cohort study, we systematically sampled health-care workers, the environment, and patients over 14 months at the ICU and HDU of the Royal Sussex County Hospital, Brighton, England. Nasal swabs were taken from health-care workers every 4 weeks, bed spaces were sampled monthly, and screening swabs were obtained from patients at admission to the ICU or HDU, weekly thereafter, and at discharge. Isolates were cultured and their whole genome sequenced, and we used the threshold of 40 single-nucleotide variants (SNVs) or fewer to define subtypes and infer recent transmission.

Findings

Between Oct 31, 2011, and Dec 23, 2012, we sampled 198 health-care workers, 40 environmental locations, and 1854 patients; 1819 isolates were sequenced. Median nasal carriage rate of S aureus in health-care workers at 4-weekly timepoints was 36·9% (IQR 35·7–37·3), and 115 (58%) health-care workers had S aureus detected at least once during the study. S aureus was identified in 8–50% of environmental samples. 605 genetically distinct subtypes were identified (median SNV difference 273, IQR 162–399) at a rate of 38 (IQR 34–42) per 4-weekly cycle. Only 25 instances of transmission to patients (seven from health-care workers, two from the environment, and 16 from other patients) were detected.

Interpretation

In the presence of standard infection control measures, health-care workers were infrequently sources of transmission to patients. S aureus epidemiology in the ICU and HDU is characterised by continuous ingress of distinct subtypes rather than transmission of genetically related strains.

Funding

UK Medical Research Council, Wellcome Trust, Biotechnology and Biological Sciences Research Council, UK National Institute for Health Research, and Public Health England.

Methicillin-ResistantStaphylococcus AureusCarriage Among Patients After Hospital Discharge

Background and Objective:

At the University Medical Center Utrecht (UMCU), follow-up implies an inventory of risk factors and screening for MRSA colonization among all MRSA-positive patients for at least 6 months. If risk factors or positive cultures persist or re-emerge, longer follow-up is indicated and isolation at readmission. This study investigated how long MRSA-positive patients remained colonized after hospital discharge and which risk factors were important. Furthermore, the results of eradication therapy were evaluated.

Design:

All patients who were positive for MRSA at the UMCU between January 1991 and January 2001 were analyzed regarding carriage state, presence of risk factors for prolonged carriage ofStaphylococcus aureus, and eradication treatment.

Results:

A total of 135 patients were included in the study. The median follow-up time was 1.2 years. Eighteen percent of the patients were dismissed from follow-up 1 year after discharge. Only 5 patients were dismissed after 6 months. Among patients with no risk factors, eradication treatment was effective for 95% within 1 year. Among patients with persistent risk factors, treatment was effective for 89% within 2 years.

Conclusions:

Based on these findings, eradication therapy should be prescribed for all MRSA carriers, independent of the presence of risk factors. MRSA-positive patients should be evaluated for 6 months for the presence of risk factors and MRSA carriage. Screening for risk factors is important because intermittent MRSA carriage was found in a significant number of our patients. Patients with negative MRSA cultures and without risk factors for 12 months can be safely dismissed from follow-up. (Infect Control Hosp Epidemiol 2005;26:629-633)

The role of healthcare personnel in the maintenance and spread of methicillin-resistant Staphylococcus aureus

Healthcare workers may acquire methicillin-resistant Staphylococcus aureus (MRSA) from patients, both hospital and home environments, other healthcare workers, family and public acquaintances, and pets. There is a consensus of case reports and series which now strongly support the role for MRSA-carrying healthcare personnel to serve as a reservoir and as a vehicle of spread within healthcare settings. Carriage may occur at a number of body sites and for short, intermediate, and long terms. A number of approaches have been taken to interrupt the linkage of staff-patient spread, but most emphasis has been placed on handwashing and the treatment of staff MRSA carriers. The importance of healthcare workers in transmission has been viewed with varying degrees of interest, and several logistical problems have arisen when healthcare worker screening is brought to the forefront. There is now considerable support for the screening and treatment of healthcare workers, but it is suggested that the intensity of any such approach must consider available resources, the nature of the outbreak, and the strength of epidemiological associations. The task of assessing healthcare personnel carriage in any context should be shaped with due regard to national and international guidelines, should be honed and practiced according to local needs and experience, and must be patient-oriented.

Outbreak of epidemic methicillin-resistant Staphylococcus aureus in a regional burns unit: Management and implications

Colonization of burn patients with methicillin-resistant Staphylococcus aureus (MRSA) is not uncommon, however an outbreak that necessitates closure of a burns unit is relatively rare. The objective of this study was to present the experience of a regional adult burns unit where an outbreak of epidemic MRSA-15 (EMRSA-15) took place. During the studied period, 176 patients were admitted to the unit, 52 with burns, 48 for elective plastic surgery procedures while the remainder belonged to other specialties. Patients admitted under burns and plastic surgery were investigated together with 46 staff members to control the outbreak. MRSA was isolated in 18 patients out of which 12 had EMRSA-15. Among the staff members, MRSA was isolated in nine of which five had EMRSA-15. The burns unit was closed to all admissions to terminate this outbreak. The MRSA positive staff members were sent on "special leave" and underwent treatment with nasal mupirocin and triclosan body wash. All staff members were able to return to work after one week's treatment. The burns unit underwent re-furbishment and decontamination while it was closed. In conclusion, the study shows that an outbreak of EMRSA was controlled successfully, however, it highlights the implications of such an event for a regional burn service with regard to staff, patients and guidelines for management.

MRSA at an English children's hospital from 1998 to 2003

AIMS

To investigate the epidemiological and clinical aspects of MRSA among inpatients and outpatients presenting to hospital.

METHODS

Analysis of demographic, epidemiological, and clinical data collected on 385 children first identified as having MRSA between January 1998 and December 2003 in a 250 bed English children's hospital.

RESULTS

There were 267 inpatients and 118 outpatients. The number of new cases of MRSA declined from 72 in 1998 to 52 in 2003, whereas hospital activity increased. Ninety nine (37.1%) inpatients acquired MRSA outside the hospital; a further 90 occurred among 31 clusters of cases. One hundred and seventy eight (66.7%) inpatients were aged <2 years; cardiac services and paediatric & neonatal surgery accounted for 59.6% of cases. Dermatology and A&E accounted for 51.7% of outpatients; 73.8% of outpatients had recently previously attended the hospital. A total of 13.9% of inpatients with MRSA developed bacteraemia; MRSA accounted for 15% of Staphylococcus aureus bacteraemias. The risk of MRSA bacteraemia in colonised patients, and the proportion of S aureus bacteraemias that were MRSA, varied between specialties. Intravascular devices were the most common source of MRSA bacteraemia (63.4% of cases). The mortality rate was 7.3%.

CONCLUSIONS

Enhanced surveillance of MRSA can identify at-risk patient groups, thus facilitating targeting of control measures. The absence of a link between numbers of cases of acquisition of MRSA and bacteraemia suggests that the rise in MRSA bacteraemia may not solely reflect an increase in MRSA prevalence in children in the UK. The need for larger epidemiological studies is emphasised.

Bed, bath and beyond: pitfalls in prompt eradication of methicillin-resistant Staphylococcus aureus carrier status in healthcare workers

Healthcare workers (HCWs) in close contact with patients colonized with methicillin-resistant Staphylococcus aureus (MRSA) were screened for MRSA acquisition. From 1995 to 2001, MRSA was identified from the nasopharyngeal swabs of 87 HCWs, collected one to two weeks after contact with 592 known MRSA-positive patients. These HCWs were withdrawn from work and treated with topical antibiotics/antiseptics. They were advised to disinfect their bathrooms and personal hygiene articles, and to wash bed linen and pillows. They were screened for successful eradication for up to three months. Seventy-three (84%) HCWs lost their carrier status. The eradication regimen failed in 14 cases. In 11 of these MRSA was detected only in later nasopharyngeal swabs (suspected recolonization). Screening identified nasal colonization of close household contacts in eight of these 11 cases. Environmental sampling detected contamination in seven out of eight screened home environments. When eradication treatment was applied to household contacts and when household surfaces were cleaned and disinfected, the carriage cleared in most cases within a few weeks. However, when home environments are heavily contaminated, despite adequate medical treatment, eradication took upto two years. Due to withdrawal from work, the 14 carriers without prompt and lasting eradication after the first course of treatment accounted for about 70% of all lost working days. These experiences support the hypothesis that control measures should not be restricted to antibiotic or antiseptic treatment of long-term carriers (HCWs as well as patients), but must also include cleaning and disinfection of the household.

Methicillin-resistant Staphylococcus aureus in orthopaedic surgery

We prospectively studied the incidence of methicillin-resistant Staphylococcus aureus (MRSA) colonisation and infection, the patterns and types of operation associated with MRSA acquisition in an orthopaedic and trauma unit in London, UK. Over the 12-month study period from January to December 2000, we found that 1.6% of the total admission was diagnosed to be either MRSA infected or colonised, with an average of three new MRSA cases detected per month. A significant proportion of patients (23%) were diagnosed within the first 48h of admission. Both hip joint surgery, especially emergency procedures for femoral neck fractures, and the presence of a wound presented higher risk of infection. The Intensive Care Unit (ICU) did not appear to be a significant source for intra-hospital dissemination among the orthopaedic patients. MRSA infection or colonisation contributed to an increased length of hospital stay; 88 days compared to 11 days on average for non-MRSA patients; 41% of the positive patients still carried MRSA on discharge. Our data show the importance of diagnosing MRSA in orthopaedic surgery and emphasises that understanding its epidemiology will be crucial to secure a decrease in the incidence of MRSA. Hand hygiene, patient screening, careful surveillance of infections and the prompt implementation of isolation policies, are essential components of control.

Role of healthcare workers in outbreaks of methicillin-resistant Staphylococcus aureus: a 10-year evaluation from a Dutch university hospital

BACKGROUND AND OBJECTIVE

The benefit of screening healthcare workers (HCWs) at risk for methicillin-resistant Staphylococcus aureus (MRSA) carriage and furloughing MRSA-positive HCWs to prevent spread to patients is controversial. We evaluated our MRSA program for HCWs between 1992 and 2002.

SETTING

A university medical center in The Netherlands, where methicillin resistance has been kept below 0.5% of all nosocomial S. aureus infections using active surveillance cultures and isolation of colonized patients.

DESIGN

HCWs caring for MRSA-positive patients or patients in foreign hospitals were screened for MRSA. MRSA-positive HCWs had additional cultures, temporary exclusion from patient-related work, assessment of risk factors for persisting carriage, decolonization therapy with mupirocin intranasally and chlorhexidine baths for skin and hair, and follow-up cultures.

RESULTS

Fifty-nine HCWs were colonized with MRSA. Seven of 840 screened employees contracted MRSA in foreign hospitals; 36 acquired MRSA after contact with MRSA-positive patients despite isolation precautions (attack rate per outbreak varied from less than 1% to 15%). Our hospital experienced 17 MRSA outbreaks, including 13 episodes in which HCWs were involved. HCWs were index cases of at least 4 outbreaks. In 8 outbreaks, HCWs acquired MRSA after caring for MRSA-positive patients despite isolation precautions.

CONCLUSION

Postexposure screening of HCWs allowed early detection of MRSA carriage and prevention of subsequent transmission to patients. Where the MRSA prevalence is higher, the role of HCWs may be greater. In such settings, an adapted version of our program could help prevent dissemination.

Staphylococcus aureus Carriage and Health Care-acquired Infection

Staphylococcus aureus is one of the most common nosocomial pathogens. Its propensity to establish prolonged carriage among hospitalized patients and increasing resistance to antibiotics makes control of this organism within the hospital difficult. High-level vancomycin resistance has now been reported in a single clinical isolate of S. aureus, emphasizing the need to increase efforts to control nosocomial spread. Knowledge of the epidemiology of S. aureus colonization among patients has shed new light on the potential difficulties in interrupting nosocomial transmission. Effective control of S. aureus within the hospital and community will require more aggressive measures that include earlier diagnosis of colonized patients, better handwashing and barrier precaution measures, and renewed efforts to eradicate the carriage state.

A purpose built MRSA cohort unit

The control of hospital-acquired infection, in particular methicillin-resistant Staphylococcus aureus (MRSA) remains a challenge. Our hospital has established a purpose built 11-bed cohort unit with on-site rehabilitation for care of patients colonized with MRSA, in an attempt to improve their quality of care. Prior to the opening of this unit a number of concerns were voiced and the aim of this study was to address these. First, to establish if patient cohorting reduces the likelihood of successful decolonization, second, to evaluate the risk of staff colonization, and finally to see if successful environmental control of MRSA is possible.A patient database was established detailing patient demographics, infection rates, eradication and reacquisition rates. Staff screening was performed weekly, at the start of a period of duty. Sixty environmental sites were screened before unit opening, at 48h, six weeks and at six months. There were 88 admissions in the first six months; 62 patients were colonized with MRSA, and 26 patients (10 surgical, 16 medical) had MRSA infections. Twenty-three of 88 patients (26%) were successfully decolonized, which compares favourably with an eradication rate of 20% for the rest of the hospital. Twenty staff members participated in weekly screening. Five staff members colonized with MRSA were detected and all were successfully decolonized. Environmental control was achieved with a combination of a daily detergent clean and a once weekly clean with phenolic disinfectant. Our preliminary data suggest that, despite cohorting patients colonized with MRSA, with proper education and supervised cleaning protocols, it is possible to control environmental MRSA load, successfully decolonize patients and limit the risk of staff colonization.

Determining risk factors for methicillin-resistant Staphylococcus aureus carriage after discharge from hospital

At the University Medical Center, Utrecht, methicillin-resistant Staphylococcus aureus (MRSA) patients are considered lifelong MRSA carriers and potentially contagious when readmitted. The purpose of this study was to determine whether patients who become MRSA carriers while in hospital remain colonized after discharge, and whether risk factors for prolonged carriage exist. Thirty-six patients colonized with MRSA during three outbreaks at University Medical Center, Utrecht (group I: 1986-1989), and twenty patients already colonized with MRSA on, or during, admission to the hospital (group II: 1990-1995) were screened for MRSA in two studies. The patients had been discharged from the hospital for periods varying from 15 days to 4.6 years. MRSA was found in five (9%). Four of these patients had skin lesions (wounds), one with an external fixture. The presence of skin- and underlying diseases differed significantly between carriers and non-carriers, supporting the hypothesis that wounds are a major risk factor for long-term MRSA carriage. This study led us to revise our policy concerning readmission of former MRSA patients. We now consider that patients who contracted MRSA in the past no longer need isolation if the following two criteria are met. Absence for at least six months of open wounds, skin lesions, tracheostomy, infections and sources of infection such as abscesses and furuncles, orthopaedic implants, drains, catheters, or tubes. Three MRSA-negative sets of swabs from nose, throat, perineum, urine, and sputum taken at least one hour apart after this six-month period.

Improved recognition of MRSA case clusters by the application of molecular subtyping using pulsed-field gel electrophoresis

Methicillin-resistant Staphylococcus aureus (MRSA) is increasingly common in hospital and community populations, making the recognition of true nosocomial outbreaks more difficult. We have used pulsed-field gel electrophoresis (PFGE) with Sma I digestion to analyse retrospectively two perceived outbreaks of epidemic methicillin-resistant Staphylococcus aureus 15 (EMRSA 15) colonization. The first cluster of cases in patients and staff on a general ward (ward D) revealed three different antibiograms based on differences in ciprofloxacin and rifampicin sensitivities. All isolates typed using PFGE, which was more discriminatory than phage-typing. One PFGE banding profile labelled type 5 was predominant, but 12 isolates proved to be subtypes of type 5 and two were PFGE type 11. Four staff members carried a strain not found in patients, three carried strains found in patients and transient carriage was highlighted as a problem when screening staff. PFGE enhanced the epidemiological data and proved that the cases on this ward did not comprise one large outbreak but numerous sporadic cases and smaller clusters. In contrast, isolates from a second cluster of cases which occurred on ward F were indistinguishable using antibiograms, phage-typing and PFGE, confirming this was more likely to be a true outbreak of colonization. We conclude that PFGE usefully augments epidemiological information and allows more logical infection control decisions to be made, with better utilization of scarce resources.

New approaches to reduce Staphylococcus aureus nosocomial infection rates: treating S. aureus nasal carriage

BACKGROUND

Nosocomial infections cause significant patient morbidity and mortality. The 2.5 million nosocomial infections that occur each year cost the US healthcare system $5 million to $10 million. Staphylococcus aureus has long been recognized as an important pathogen in human disease and is the most common cause of nosocomial infections.

OBJECTIVE

To describe the epidemiology of S. aureus nosocomial infections that are attributable to patients' endogenous colonization.

DATA SOURCES

Review of the English-language literature and a MEDLINE search (as of September 1997).

DATA SYNTHESIS

The ecologic niche of S. aureus is the anterior nares. The prevalence of S. aureus nasal carriage is approximately 20-25%, but varies among different populations, and is influenced by age, underlying illness, race, certain behaviors, and the environment in which the person lives or works. The link between S. aureus nasal carriage and development of subsequent S. aureus infections has been established in patients on hemodialysis, on continuous ambulatory peritoneal dialysis, and those undergoing surgery. S. aureus nasal carriers have a two-to tenfold increased risk of developing S. aureus surgical site or intravenous catheter infections. Thirty percent of 100% of S. aureus infections are due to endogenous flora and infecting strains were genetically identical to nasal strains. Three treatment strategies may eliminate nasal carriage: locally applied antibiotics or disinfectants, systemic antibiotics, and bacterial interference. Among these strategies, locally applied or systemic antibiotics are most commonly used. Nasal ointments or sprays and oral antibiotics have variable efficacy and their use frequently results in antimicrobial resistance among S. aureus strains. Of the commonly used agents, mupirocin (pseudomonic acid) ointment has been shown to be 97% effective in reducing S. aureus nasal carriage. However, resistance occurs when the ointment has been applied for a prolonged period over large surface areas.

CONCLUSIONS

Given the importance of S. aureus nosocomial infections and the increased risk of S. aureus nasal carriage in patients with nosocomial infections, investigators need to study cost-effective strategies to prevent certain types of nosocomial infections or nosocomial infections that occur in specific settings. One potential strategy is to decrease S. aureus nasal carriage among certain patient populations.

Methicillin resistant Staphylococcus aureus in three adjacent health districts of south-east England 1986-91

The experiences with methicillin-resistant Staphylococcus aureus (MRSA) of two contiguous Health Districts during 1986-91 and of a third mutually adjacent District in south-east England during 1989-91 were compared. Although the three Districts were in many ways similar, the nature of the problems posed by MRSA differed. The Districts had dealt with MRSA independently but had evolved similar strategies for coping with the organism. In two Districts a gradual relaxation of case-finding and of infection control precautions applied to individual patients and outbreaks, was followed by a reduction in the number of new patient-isolates identified from routine bacteriology specimens. Standardization of MRSA isolation rates for patient throughput and for length of hospital stay showed the examination of crude total isolates to provide misleading comparisons of relative risks of acquiring MRSA in different specialties. It was also found that patients discharged from specialties with short inpatient stays were more likely to have MRSA detected after discharge by their physicians working in the local community served by the hospitals but there was no evidence of spread outside hospital. It is suggested that good all-round standards of infection control practice are more important than specific radical policies in dealing with endemic MRSA.