Modeling the spread of methicillin-resistant Staphylococcus aureus in nursing homes for elderly

Nasal Carriage Rate of Staphylococcus aureus, Its Associated Factors, and Antimicrobial Susceptibility Pattern Among Health Care Workers in Public Hospitals, Harar, Eastern Ethiopia

Background

Staphylococcus aureus is the bacteria that colonizes the nasal nares of health-care workers and serves as a reservoir for the spread of pathogen for subsequent infections, mainly Methicillin-resistant Staphylococcus aureus. However, there is a limited study conducted regarding this topic in Harar, Eastern Ethiopia.

Objective

The main objective of this study was to determine the prevalence of nasal carriage of Staphylococcus aureus, associated factors and antimicrobial susceptibility patterns among health-care workers of public hospitals in Harar, Eastern Ethiopia from May 15 to July 30, 2021.

Methods

A hospital-based cross-sectional study was conducted on 295 health-care workers. A simple random sampling technique was used to select the participant. Nasal swabs were collected and cultured at 35°C for 24hrs. S. aureus was identified using the coagulase test and catalase test. Methicillin resistance S. aureus (MRSA) was screened using a cefoxitin disc on Muller Hinton agar using the Kirby-Bauer disc diffusion method. Data were entered into EPI-Info version-7 and transferred to SPSS-20 for analysis. Factors associated with nasal carriage of Staphylococcus aureus were determined by using chi-square analysis. A p-value of less than 0.05 was considered statistically significant.

Results

The prevalence of Staphylococcus aureus in this study was 15.6% (95% CI: 11.7%, 20.3%) and methicillin-resistant Staphylococcus aureus was 11.2% (95% CI: 7.8%, 15.4%), respectively. Age (P < 0.001), work experience (p < 0.001), working unit (p < 0.02), antibiotic use within 3 months (p < 0.001), hand washing habit (p < 0.01), hand rub use (p < 0.001), living with smokers (p < 0.001), living with pets (p < 0.001) and having chronic diseases (p < 0.001) were found significantly associated with Staphylococcus aureus nasal carriage.

Conclusion

The prevalence of Staphylococcus aureus and Methicillin-resistant Staphylococcus aureus are high in our study. The study emphasizes the need for regular surveillance among hospital staff and the environment to prevent MRSA transmission among health-care personnel.

Impact of visitation and cohorting policies to shield residents from covid-19 spread in care homes: an agent-based model

BACKGROUND

This study examines the impact of visitation and cohorting policies as well as the care home population size upon the spread of COVID-19 and the risk of outbreak occurrence in this setting.

METHODS

Agent-based modelling RESULTS: The likelihood of the presence of an outbreak in a care home is associated with the care home population size. Cohorting of residents and staff into smaller, self-contained units reduces the spread of COVID-19. Restricting the number of visitors to the care home to shield its residents does not significantly impact the cumulative number of infected residents and risk of outbreak occurrence in most scenarios. Only when the community prevalence where staff live is considerably lower than the prevalence where visitors live (the former prevalence is less than or equal to 30% of the latter), relaxing visitation increases predicted infections much more significantly than it does in other scenarios. Maintaining a low infection probability per resident-visitor contact helps reduce the effect of allowing more visitors into care homes.

CONCLUSIONS

Our model predictions suggest that cohorting is effective in controlling the spread of COVID-19 in care homes. However, according to predictions shielding residents in care homes is not as effective as predicted in a number of studies that have modelled shielding of vulnerable population in the wider communities.

Evaluating intervention strategies in controlling coronavirus disease 2019 (COVID-19) spread in care homes: An agent-based model

BACKGROUND

Care homes are vulnerable to widespread transmission of severe acute respiratory coronavirus virus 2 (SARS-CoV-2) with poor outcomes for staff and residents. Infection control interventions in care homes need to not only be effective in containing the spread of coronavirus disease 2019 (COVID-19) but also feasible to implement in this special setting which is both a healthcare institution and a home.

METHODS

We developed an agent-based model that simulates the transmission dynamics of COVID-19 via contacts between individuals, including residents, staff members, and visitors in a care home setting. We explored a representative care home in Scotland in our base case and explore other care home setups in an uncertainty analysis. We evaluated the effectiveness of a range of intervention strategies in controlling the spread of COVID-19.

RESULTS

In the presence of the reference interventions that have been implemented in many care homes, including testing of new admissions, isolation of symptomatic residents, and restricted public visiting, routine testing of staff appears to be the most effective and practical approach. Routine testing of residents is no more effective as a reference strategy while routine testing of both staff and residents only shows a negligible additive effect. Modeling results are very sensitive to transmission probability per contact, but the qualitative finding is robust to varying parameter values in our uncertainty analysis.

CONCLUSIONS

Our model predictions suggest that routine testing should target staff in care homes in conjunction with adherence to strict hand hygiene and using personal protective equipment to reduce risk of transmission per contact.

Synergistic Effect of Combination Interventions for Methicillin-Resistant Staphylococcus aureus Transmission Control in Nursing Homes: A Computation Modelling Evaluation with Heterogeneous Contact Mixing

The endemic threat of methicillin-resistant Staphylococcus aureus (MRSA) in nursing homes poses a serious and escalating challenge to public health administration in infection control. Nursing homes are considered as major reservoirs for MRSA colonization, with considerable high levels of colonization prevalence. We employed a computation model to evaluate effects of three intervention scenarios on MRSA colonization prevalence rate in nursing homes. Simulations were conducted using a deterministic compartmental model featuring heterogeneous contact matrix between residents and health-care workers (HCWs). Contact parameters were derived from a nursing home survey. Three intervention scenarios were simulated: (1) hand-hygiene compliance by HCWs, (2) screening-and-isolation upon admission, and (3) implementing both interventions at the same time. For every 10% reduction in average contamination duration in HCWs, the estimated average reduction in prevalence rate was 1.29 percentage point compared with the prevalence rate before the intervention was implemented. Screening-and-isolation intervention resulted in an average reduction of 19.04 percentage point in prevalence rate (S.D. = 1.58; 95% CI = 18.90-19.18). In intervention scenario 3, synergistic effects were observed when implementing hand-hygiene compliance by HCWs and screening-and-isolation together. Our results provide evidence showing that implementing multiple interventions together has a synergistic effect on colonization prevalence reduction.

Transmission and Long-Term Colonization Patterns of Staphylococcus aureus in a Nursing Home

Nursing homes might create an environment favorable for the transmission of Staphylococcus aureus because of the presence of hospitalized elderly, overcrowding and close contacts among people. We aimed at identifying risk factors for S. aureus colonization and determining the genetic relatedness of isolates demonstrating transmission among people. We investigated 736 swab samples from 92 residents and personnel for the presence of S. aureus. Swabs from anterior nares and throat were collected quarterly (2018) in a nursing home located in Poland. Genotyping was conducted using the multi-locus variable number of tandem repeats fingerprinting (MLVF) method. We observed high seasonal variation in the proportion of participants colonized with methicillin-resistant Staphylococcus aureus (MRSA) strains (0% to 13.5%). A multivariate analysis revealed that residents aged more than 85 years old are at risk for becoming intermittent S. aureus carriers (p = 0.013). The MLVF analysis revealed a high genetic diversity among methicillin-sensitive S. aureus (MSSA) strains and close genetic relatedness between MRSA strains. We proved the advanced aged were predisposed to intermittent S. aureus carriage. Genotyping revealed the transmission of S. aureus among the participants living in a closed environment. A high genetic relatedness among isolated MRSA suggests its clonal spread in the nursing home.

Simulation models for transmission of health care-associated infection: A systematic review

BACKGROUND

Health care-associated infections (HAIs) are a global health burden because of their significant impact on patient health and health care systems. Mechanistic simulation modeling that captures the dynamics between patients, pathogens, and the environment is increasingly being used to improve understanding of epidemiological patterns of HAIs and to facilitate decisions on infection prevention and control (IPC). The purpose of this review is to present a systematic review to establish (1) how simulation models have been used to investigate HAIs and their mitigation and (2) how these models have evolved over time, as well as identify (3) gaps in their adoption and (4) useful directions for their future development.

METHODS

The review involved a systematic search and identification of studies using system dynamics, discrete event simulation, and agent-based model to study HAIs.

RESULTS

The complexity of simulation models developed for HAIs significantly increased but heavily concentrated on transmission dynamics of methicillin-resistant Staphylococcus aureus in the hospitals of high-income countries. Neither HAIs in other health care settings, the influence of contact networks within a health care facility, nor patient sharing and referring networks across health care settings were sufficiently understood.

CONCLUSIONS

This systematic review provides a broader overview of existing simulation models in HAIs to identify the gaps and to direct and facilitate further development of appropriate models in this emerging field.

Effects of the proportion of high-risk patients and control strategies on the prevalence of methicillin-resistant Staphylococcus aureus in an intensive care unit

Background

The presence of nosocomial pathogens in many intensive care units poses a threat to patients and public health worldwide. Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen endemic in many hospital settings. Patients who are colonized with MRSA may develop an infection that can complicate their prior illness.

Methods

A mathematical model to describe transmission dynamics of MRSA among high-risk and low-risk patients in an intensive care unit (ICU) via hands of health care workers is developed. We aim to explore the effects of the proportion of high-risk patients, the admission proportions of colonized and infected patients, the probability of developing an MRSA infection, and control strategies on MRSA prevalence among patients.

Results

The increasing proportion of colonized and infected patients at admission, along with the higher proportion of high-risk patients in an ICU, may significantly increase MRSA prevalence. In addition, the prevalence becomes higher if patients in the high-risk group are more likely to develop an MRSA infection. Our results also suggest that additional infection prevention and control measures targeting high-risk patients may considerably help reduce MRSA prevalence as compared to those targeting low-risk patients.

Conclusions

The proportion of high-risk patients and the proportion of colonized and infected patients in the high-risk group at admission may play an important role on MRSA prevalence. Control strategies targeting high-risk patients may help reduce MRSA prevalence.

Assessment of the potential for pathogen dispersal during high-flow nasal therapy

High-flow nasal therapy is increasingly used in hospitals because of its effectiveness and patient comfort. However, pathogens in the patient's nasal and oral cavities may be dispersed by forced air. This study aimed to investigate the risk of pathogen dispersal during high-flow nasal therapy. Liquid and bacterial dispersal were assessed via in-vitro experimental set-ups using a manikin. Thickened water or fresh yeast solution mimicked saliva and nasal mucus secretions. Dispersal was limited to the proximal area of the face and nasal cannula, suggesting that high-flow nasal therapy does not increase the risk of droplet and contact infection.

A unified stochastic modelling framework for the spread of nosocomial infections

Over the last years, a number of stochastic models have been proposed for analysing the spread of nosocomial infections in hospital settings. These models often account for a number of factors governing the spread dynamics: spontaneous patient colonization, patient–staff contamination/colonization, environmental contamination, patient cohorting or healthcare workers (HCWs) hand-washing compliance levels. For each model, tailor-designed methods are implemented in order to analyse the dynamics of the nosocomial outbreak, usually by means of studying quantities of interest such as the reproduction number of each agent in the hospital ward, which is usually computed by means of stochastic simulations or deterministic approximations. In this work, we propose a highly versatile stochastic modelling framework that can account for all these factors simultaneously, and which allows one to exactly analyse the reproduction number of each agent at the hospital ward during a nosocomial outbreak. By means of five representative case studies, we show how this unified modelling framework comprehends, as particular cases, many of the existing models in the literature. We implement various numerical studies via which we (i) highlight the importance of maintaining high hand-hygiene compliance levels by HCWs, (ii) support infection control strategies including to improve environmental cleaning during an outbreak and (iii) show the potential of some HCWs to act as super-spreaders during nosocomial outbreaks.

Population-level mathematical modeling of antimicrobial resistance: a systematic review

BACKGROUND

Mathematical transmission models are increasingly used to guide public health interventions for infectious diseases, particularly in the context of emerging pathogens; however, the contribution of modeling to the growing issue of antimicrobial resistance (AMR) remains unclear. Here, we systematically evaluate publications on population-level transmission models of AMR over a recent period (2006-2016) to gauge the state of research and identify gaps warranting further work.

METHODS

We performed a systematic literature search of relevant databases to identify transmission studies of AMR in viral, bacterial, and parasitic disease systems. We analyzed the temporal, geographic, and subject matter trends, described the predominant medical and behavioral interventions studied, and identified central findings relating to key pathogens.

RESULTS

We identified 273 modeling studies; the majority of which (> 70%) focused on 5 infectious diseases (human immunodeficiency virus (HIV), influenza virus, Plasmodium falciparum (malaria), Mycobacterium tuberculosis (TB), and methicillin-resistant Staphylococcus aureus (MRSA)). AMR studies of influenza and nosocomial pathogens were mainly set in industrialized nations, while HIV, TB, and malaria studies were heavily skewed towards developing countries. The majority of articles focused on AMR exclusively in humans (89%), either in community (58%) or healthcare (27%) settings. Model systems were largely compartmental (76%) and deterministic (66%). Only 43% of models were calibrated against epidemiological data, and few were validated against out-of-sample datasets (14%). The interventions considered were primarily the impact of different drug regimens, hygiene and infection control measures, screening, and diagnostics, while few studies addressed de novo resistance, vaccination strategies, economic, or behavioral changes to reduce antibiotic use in humans and animals.

CONCLUSIONS

The AMR modeling literature concentrates on disease systems where resistance has been long-established, while few studies pro-actively address recent rise in resistance in new pathogens or explore upstream strategies to reduce overall antibiotic consumption. Notable gaps include research on emerging resistance in Enterobacteriaceae and Neisseria gonorrhoeae; AMR transmission at the animal-human interface, particularly in agricultural and veterinary settings; transmission between hospitals and the community; the role of environmental factors in AMR transmission; and the potential of vaccines to combat AMR.

Nasal carriage, risk factors and antimicrobial susceptibility pattern of methicillin resistant Staphylococcus aureus among healthcare workers in Adigrat and Wukro hospitals, Tigray, Northern Ethiopia

Objective

The aim of this study was to determine nasal carriage, risk factors and antimicrobial susceptibility pattern of methicillin resistant Staphylococcus aureus among health care-workers of Adigrat and Wukro hospitals Northern Ethiopia.

Results

The overall prevalence of S. aureus and methicillin resistance S. aureus (MRSA) in the present study were 12% (29/242) and 5.8% (14/242) respectively. The rate of MRSA among S. aureus was 48.3%(14/29). In this study, MRSA carriage was particularly higher among nurse professionals (7.8%) and surgical ward (17.1%). None of the MRSA isolates were sensitive to penicillin and ampicillin. However, low resistance was found for chloramphenicol and clindamycin. Being diabetic and use of hands rub was statistically significant with MRSA colonization.

Electronic supplementary material

The online version of this article (10.1186/s13104-018-3353-2) contains supplementary material, which is available to authorized users.

A systematic review of transmission dynamic studies of methicillin-resistant Staphylococcus aureus in non-hospital residential facilities

BACKGROUND

Non-hospital residential facilities are important reservoirs for MRSA transmission. However, conclusions and public health implications drawn from the many mathematical models depicting nosocomial MRSA transmission may not be applicable to these settings. Therefore, we reviewed the MRSA transmission dynamics studies in defined non-hospital residential facilities to: (1) provide an overview of basic epidemiology which has been addressed; (2) identify future research direction; and (3) improve future model implementation.

METHODS

A review was conducted by searching related keywords in PUBMED without time restriction as well as internet searches via Google search engine. We included only articles describing the epidemiological transmission pathways of MRSA/community-associated MRSA within and between defined non-hospital residential settings.

RESULTS

Among the 10 included articles, nursing homes (NHs) and correctional facilities (CFs) were two settings considered most frequently. Importation of colonized residents was a plausible reason for MRSA outbreaks in NHs, where MRSA was endemic without strict infection control interventions. The importance of NHs over hospitals in increasing nosocomial MRSA prevalence was highlighted. Suggested interventions in NHs included: appropriate staffing level, screening and decolonizing, and hand hygiene. On the other hand, the small population amongst inmates in CFs has no effect on MRSA community transmission. Included models ranged from system-level compartmental models to agent-based models. There was no consensus over the course of disease progression in these models, which were mainly featured with NH residents /CF inmates/ hospital patients as transmission pathways. Some parameters used by these models were outdated or unfit.

CONCLUSIONS

Importance of NHs has been highlighted from these current studies addressing scattered aspects of MRSA epidemiology. However, the wide variety of non-hospital residential settings suggest that more work is needed before robust conclusions can be drawn. Learning from existing work for hospitals, we identified critical future research direction in this area from infection control, ecological and economic perspectives. From current model deficiencies, we suggest more transmission pathways be specified to depict MRSA transmission, and further empirical studies be stressed to support evidence-based mathematical models of MRSA in non-hospital facilities. Future models should be ready to cope with the aging population structure.

A unified inter-host and in-host model of antibiotic resistance and infection spread in a hospital ward

As the battle continues against hospital-acquired infections and the concurrent rise in antibiotic resistance among many of the major causative pathogens, there is a dire need to conduct controlled experiments, in order to compare proposed control strategies. However, cost, time, and ethical considerations make this evaluation strategy either impractical or impossible to implement with living patients. This paper presents a multi-scale model that offers promise as the basis for a tool to simulate these (and other) controlled experiments. This is a "unified" model in two important ways: (i) It combines inter-host and in-host dynamics into a single model, and (ii) it links two very different modeling approaches - agent-based modeling and differential equations - into a single model. The potential of this model as an instrument to combat antibiotic resistance in hospitals is demonstrated with numerical examples.

Understanding the Impact of Interventions to Prevent Antimicrobial Resistant Infections in the Long-Term Care Facility: A Review and Practical Guide to Mathematical Modeling

OBJECTIVES (1) To systematically search for all dynamic mathematical models of infectious disease transmission in long-term care facilities (LTCFs); (2) to critically evaluate models of interventions against antimicrobial resistance (AMR) in this setting; and (3) to develop a checklist for hospital epidemiologists and policy makers by which to distinguish good quality models of AMR in LTCFs. METHODS The CINAHL, EMBASE, Global Health, MEDLINE, and Scopus databases were systematically searched for studies of dynamic mathematical models set in LTCFs. Models of interventions targeting methicillin-resistant Staphylococcus aureus in LTCFs were critically assessed. Using this analysis, we developed a checklist for good quality mathematical models of AMR in LTCFs. RESULTS AND DISCUSSION Overall, 18 papers described mathematical models that characterized the spread of infectious diseases in LTCFs, but no models of AMR in gram-negative bacteria in this setting were described. Future models of AMR in LTCFs require a more robust methodology (ie, formal model fitting to data and validation), greater transparency regarding model assumptions, setting-specific data, realistic and current setting-specific parameters, and inclusion of movement dynamics between LTCFs and hospitals. CONCLUSIONS Mathematical models of AMR in gram-negative bacteria in the LTCF setting, where these bacteria are increasingly becoming prevalent, are needed to help guide infection prevention and control. Improvements are required to develop outputs of sufficient quality to help guide interventions and policy in the future. We suggest a checklist of criteria to be used as a practical guide to determine whether a model is robust enough to test policy. Infect Control Hosp Epidemiol 2017;38:216-225.

Reduction of methicillin-resistant Staphylococcus aureus infection in long-term care is possible while maintaining patient socialization: A prospective randomized clinical trial

BACKGROUND

Antibiotic resistance is a challenge in long-term care facilities (LTCFs). The objective of this study was to demonstrate that a novel, minimally invasive program not interfering with activities of daily living or socialization could lower methicillin-resistant Staphylococcus aureus (MRSA) disease.

METHODS

This was a prospective, cluster-randomized, nonblinded trial initiated at 3 LTCFs. During year 1, units were stratified by type of care and randomized to intervention or control. In year 2, all units were converted to intervention consisting of universal decolonization using intranasal mupirocin and a chlorhexidine bath performed twice (2 decolonization-bathing cycles 1 month apart) at the start of the intervention period. Subsequently, after initial decolonization, all admissions were screened on site using real-time polymerase chain reaction, and those MRSA positive were decolonized, but not isolated. Units received annual instruction on hand hygiene. Enhanced bleach wipe cleaning of flat surfaces was done every 4 months.

RESULTS

There were 16,773 tests performed. The MRSA infection rate decreased 65% between baseline (44 infections during 365,809 patient days) and year 2 (12 infections during 287,847 patient days; P <.001); a significant reduction was observed at each of the LTCFs (P <.03).

CONCLUSIONS

On-site MRSA surveillance with targeted decolonization resulted in a significant decrease in clinical MRSA infection among LTCF residents.

Prevalence of Nasal Colonization by Methicillin-Resistant Staphylococcus aureus in Persons Using a Homeless Shelter in Kansas City

Nasal colonization of methicillin-resistant Staphylococcus aureus (MRSA) plays an important role in the epidemiology and pathogenesis of disease. Situations of close-quarter contact in groups are generally regarded as a risk factor for community-acquired MRSA strains due to transmission via fomites and person-to-person contact. With these criteria for risk, homeless individuals using shelter facilities, including showers and toilets, should be considered high risk for colonization and infection. The aim of this study was to determine the prevalence of nasal colonization of MRSA in a homeless population compared to established rates of colonization within the public and a control group of subjects from a neighboring medical school campus, and to analyze phylogenetic diversity among the MRSA strains. Nasal samples were taken from the study population of 332 adult participants and analyzed. In addition, participants were surveyed about various lifestyle factors in order to elucidate potential patterns of behavior associated with MRSA colonization. Homeless and control groups both had higher prevalence of MRSA (9.8 and 10.6%, respectively), when compared to the general population reported by previous studies (1.8%). However, the control group had a similar MRSA rate compared to health-care workers (4.6%), while the homeless population had an increased prevalence. Risk factors identified in this study included male gender, age over 50 years, and use of antibiotics within the past 3 months. Phylogenetic relationships between nine of the positive samples from the homeless population were analyzed, showing eight of the nine samples had a high degree of relatedness between the spaA genes of the MRSA strains. This indicates that the same MRSA strain might be transmitted from person-to-person among homeless population. These findings increase our understanding of key differences in MRSA characteristics within homeless populations, as well as risks for MRSA associated with being homeless, such as age and gender, which may then be a useful tool in guiding more effective prevention, treatment, and health care for homeless individuals.

Identifying conditions for elimination and epidemic potential of methicillin-resistant Staphylococcus aureus in nursing homes

BACKGROUND

Residents of nursing homes are commonly colonized with methicillin-resistant Staphylococcus aureus (MRSA) but there is a limited understanding of the dynamics and determinants of spread in this setting. To address this gap, we sought to use mathematical modeling to assess the epidemic potential of MRSA in nursing homes and to determine conditions under which non-USA300 and USA300 MRSA could be eliminated or reduced in the facilities.

METHODS

Model parameters were estimated from data generated during a longitudinal study of MRSA in 6 Wisconsin nursing homes. The data included subject colonization status with strain-specific MRSA collected every 3 months for up to 1 year. Deterministic and stochastic co-colonization and single-strain models were developed to describe strain-specific dynamics of MRSA in these facilities. Basic reproduction numbers of strain-independent MRSA, non-USA300 and USA300 MRSA were estimated numerically. The impact of antibiotic use in the past 3 months on the prevalence of strain-specific MRSA and associated basic reproduction numbers were evaluated.

RESULTS

Our models predicted that MRSA would persist in Wisconsin nursing homes, and non-USA300 would remain the dominant circulating strain. MRSA eradication was theoretically achievable by elimination of MRSA-positive admissions over the course of years. Substantial reductions in MRSA prevalence could be attained through marked increase in clearance rates or reduction in MRSA-positive admissions sustained over years. The basic reproduction number of strain-independent MRSA was 0.18 (95 % CI = 0.13-0.23). Recent antibiotic use increased the prevalence of strain-specific MRSA and associated basic reproduction numbers, but was unlikely to lead to an outbreak.

CONCLUSIONS

Based on our model, MRSA elimination from nursing homes, while theoretically possible, was unlikely to be achieved in practice. Decolonization therapy that can sustain higher clearance rates or lower MRSA-positive introductions over years may reduce strain-specific prevalence of MRSA in the facilities, and antibiotic stewardship may contribute to this effort. Large-scale MRSA outbreaks were unlikely in this setting.

Risk factors for methicillin-resistant Staphylococcus aureus carriage among residents in 7 nursing homes in Shanghai, China

BACKGROUND

Nursing home residents are a population at risk for methicillin-resistant Staphylococcus aureus (MRSA) carriage, but few data about MRSA in this setting in Shanghai are available. The aim of this study is to determine the prevalence and risk factors for MRSA carriage in nursing home residents in Shanghai, China.

METHODS

Four hundred forty-three residents from 7 nursing homes in Shanghai, China, participated in this study; nasal and axillary swabs were obtained from these residents. Laboratory identification for S aureus and antimicrobial susceptibility testing were performed when isolated. Data, including individual resident characteristics and nursing home characteristics, were collected and analyzed.

RESULTS

Of the 443 participating residents, 99 (22.3%) and 45 (10.2%) residents were colonized by S aureus and MRSA, respectively. Previous hospitalization (odds ratio [OR], 2.564; 95% confidence interval [CI], 1.214-5.415; P = .014), presence of an invasive device (OR, 3.455; 95% CI, 1.678-7.113; P = .001), chloramphenicol therapy (OR, 7.672; 95% CI, 1.807-32.580; P = .006), and macrolides therapy (OR, 2.796; 95% CI, 1.056-7.403; P = .038) were independent risk factors for MRSA colonization. Low expenditure per month and less good sanitary condition also increased the risk for MRSA colonization.

CONCLUSIONS

Our study suggests that nursing homes are significant reservoirs for MRSA. Implementation of infection control strategies must be given high priority in nursing homes to fight the high prevalence of MRSA, and increased convenience and feasibility should also be realized with these control strategies for MRSA colonization.

A metapopulation model for the spread of MRSA in correctional facilities

The spread of methicillin-resistant strains of Staphylococcus aureus (MRSA) in health-care settings has become increasingly difficult to control and has since been able to spread in the general community. The prevalence of MRSA within the general public has caused outbreaks in groups of people in close quarters such as military barracks, gyms, daycare centres and correctional facilities. Correctional facilities are of particular importance for spreading MRSA, as inmates are often in close proximity and have limited access to hygienic products and clean clothing. Although these conditions are ideal for spreading MRSA, a recent study has suggested that recurrent epidemics are caused by the influx of colonized or infected individuals into the correctional facility. In this paper, we further investigate the effects of community dynamics on the spread of MRSA within the correctional facility and determine whether recidivism has a significant effect on disease dynamics. Using a simplified hotspot model ignoring disease dynamics within the correctional facility, as well as two metapopulation models, we demonstrate that outbreaks in correctional facilities can be driven by community dynamics even when spread between inmates is restricted. We also show that disease dynamics within the correctional facility and their effect on the outlying community may be ignored due to the smaller size of the incarcerated population. This will allow construction of simpler models that consider the effects of many MRSA hotspots interacting with the general community. It is suspected that the cumulative effects of hotspots for MRSA would have a stronger feedback effect in other community settings.

Prevalence and Molecular Epidemiology of Staphylococcus aureus among Residents of Seven Nursing Homes in Shanghai

BACKGROUND

Residents in nursing homes (NHs) always represent potential reservoirs for Staphylococcus aureus and methicillin-resistant S. aureus (MRSA). To our knowledge, there is no epidemiological information up till now that describes the prevalence and molecular characteristics of S. aureus in nursing home residents in Shanghai, China.

METHODS

Four hundred and ninety-one unique residents from 7 NHs were enrolled in this study. Specimens were collected among these residents including 491 nasal swabs, 487 axillary swabs and 119 skin swabs. S. aureus isolated and identified from the swabs was characterized according to antimicrobial susceptibility profiling, toxin gene prevalence, and multilocus sequence typing (MLST), spa and SCCmec typing.

RESULTS

Among the 491 residents screened, S. aureus was isolated in 109 residents from 90 nasal swabs (90/491, 18.3%), 29 axillary swabs (29/487, 6.0%), and 22 skin swabs (22/119, 18.5%). Sixty-eight MRSA isolates were detected in 52 residents from 41 nasal carriers, 15 axillary carriers and 12 skin carriers. The overall prevalence rate of S. aureus and MRSA colonization was 22.2% and 10.6% respectively. Ten residents presented S. aureus in all three sample types and 12 residents presented S. aureus in two of the three sample types collected. Molecular analysis revealed CC1 (29.1%) to be the dominant clone in this study, followed by CC398 (19.9%), CC188 (13.5%) and CC5 (12.8%). The most common spa type was t127 (22.0%), followed by t14383 (12.8%) and t002 (10.6%).

CONCLUSIONS

A high prevalence of S. aureus and MRSA colonization was revealed in nursing home residents in Shanghai. CC1 was the most common clonal complex and t127 was the most common spa type among NH residents. The data provides an important baseline for future surveillance of S. aureus in NHs in Shanghai and other highly urbanized regions in China. Implementation of infection control strategies must be given high priority in NHs to fight such high prevalence of both MRSA and methicillin-susceptible S. aureus (MSSA).

Molecular and phenotypic characterization of methicillin-resistant Staphylococcus aureus isolates causing bacteremia at a major hospital in southern Mississippi

Staphylococcus aureus is the predominant cause of bacteremia worldwide. We assessed the molecular epidemiology and antibiotic resistance of methicillin-resistant S aureus isolates causing bacteremia in southern Mississippi. Diverse genetic backgrounds in terms of staphylococcal cassette chromosome mec, pulsed-field gel electrophoresis, and multilocus sequence typing types of methicillin-resistant S aureus were identified as causing bacteremia in Mississippi. A strong association of Panton-Valentine leukocidin genes with elevated vancomycin minimum inhibitory concentration is one of the important findings of our study.

What should be considered if you decide to build your own mathematical model for predicting the development of bacterial resistance? Recommendations based on a systematic review of the literature

Acquired bacterial resistance is one of the causes of mortality and morbidity from infectious diseases. Mathematical modeling allows us to predict the spread of resistance and to some extent to control its dynamics. The purpose of this review was to examine existing mathematical models in order to understand the pros and cons of currently used approaches and to build our own model. During the analysis, seven articles on mathematical approaches to studying resistance that satisfied the inclusion/exclusion criteria were selected. All models were classified according to the approach used to study resistance in the presence of an antibiotic and were analyzed in terms of our research. Some models require modifications due to the specifics of the research. The plan for further work on model building is as follows: modify some models, according to our research, check all obtained models against our data, and select the optimal model or models with the best quality of prediction. After that we would be able to build a model for the development of resistance using the obtained results.

Optimizing hospital infection control: the role of mathematical modeling

Multidrug-resistant bacteria are major causes of nosocomial infections and are associated with considerable morbidity, mortality, and healthcare costs. Preventive strategies have therefore become increasingly important. Mathematical modeling has been widely used to understand the transmission dynamics of nosocomial infections and the quantitative effects of infection control measures. This review will explore the principles of mathematical modeling used in nosocomial infections and discuss the effectiveness of infection control measures investigated using mathematical modeling.

Protective effect of methicillin-susceptible Staphylococcus aureus carriage against methicillin-resistant S. aureus acquisition in nursing homes: a prospective cross-sectional study

OBJECTIVE

To evaluate whether an ecologic inverse association exists between methicillin-susceptible Staphylococcus aureus (MSSA) prevalence and methicillin-resistant S. aureus (MRSA) prevalence in nursing homes.

METHODS

We conducted a secondary analysis of a prospective cross-sectional study of S. aureus prevalence in 26 nursing homes across Orange County, California, from 2008-2011. Admission prevalence was assessed using bilateral nares swabs collected from all new residents within 3 days of admission until 100 swabs were obtained. Point prevalence was assessed from a representative sample of 100 residents. Swab samples were plated on 5% sheep blood agar and Spectra MRSA chromogenic agar. If MRSA was detected, no further tests were performed. If MRSA was not detected, blood agar was evaluated for MSSA growth. We evaluated the association between MRSA and MSSA admission and point prevalence using correlation and linear regression testing.

RESULTS

We collected 3,806 total swabs. MRSA and MSSA admission prevalence were not correlated (r = -0.40, P = .09). However, MRSA and MSSA point prevalence were negatively correlated regardless of whether MSSA prevalence was measured among all residents sampled (r = -0.67, P = .0002) or among those who did not harbor MRSA (r = -0.41, P = .04). This effect persisted in regression models adjusted for the percentage of residents with diabetes (β = -0.73, P = .04), skin lesions (β = -1.17, P = .002), or invasive devices (β = -1.4, P = .0006).

CONCLUSIONS

The inverse association between MRSA and MSSA point prevalence and minimal association on admission prevalence suggest MSSA carriage may protect against MRSA acquisition in nursing homes. The minimal association on admission prevalence further suggests competition may occur during nursing home stays.

Modeling the transmission of community-associated methicillin-resistant Staphylococcus aureus: a dynamic agent-based simulation

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) has been a deadly pathogen in healthcare settings since the 1960s, but MRSA epidemiology changed since 1990 with new genetically distinct strain types circulating among previously healthy people outside healthcare settings. Community-associated (CA) MRSA strains primarily cause skin and soft tissue infections, but may also cause life-threatening invasive infections. First seen in Australia and the U.S., it is a growing problem around the world. The U.S. has had the most widespread CA-MRSA epidemic, with strain type USA300 causing the great majority of infections. Individuals with either asymptomatic colonization or infection may transmit CA-MRSA to others, largely by skin-to-skin contact. Control measures have focused on hospital transmission. Limited public health education has focused on care for skin infections.

METHODS

We developed a fine-grained agent-based model for Chicago to identify where to target interventions to reduce CA-MRSA transmission. An agent-based model allows us to represent heterogeneity in population behavior, locations and contact patterns that are highly relevant for CA-MRSA transmission and control. Drawing on nationally representative survey data, the model represents variation in sociodemographics, locations, behaviors, and physical contact patterns. Transmission probabilities are based on a comprehensive literature review.

RESULTS

Over multiple 10-year runs with one-hour ticks, our model generates temporal and geographic trends in CA-MRSA incidence similar to Chicago from 2001 to 2010. On average, a majority of transmission events occurred in households, and colonized rather than infected agents were the source of the great majority (over 95%) of transmission events. The key findings are that infected people are not the primary source of spread. Rather, the far greater number of colonized individuals must be targeted to reduce transmission.

CONCLUSIONS

Our findings suggest that current paradigms in MRSA control in the United States cannot be very effective in reducing the incidence of CA-MRSA infections. Furthermore, the control measures that have focused on hospitals are unlikely to have much population-wide impact on CA-MRSA rates. New strategies need to be developed, as the incidence of CA-MRSA is likely to continue to grow around the world.

On the Markovian approach for modeling the dynamics of nosocomial infections

We analyze the dynamics of nosocomial infections in intensive care units (ICUs) by using a Markov chain model. Since population size in the ICU is small, in contrast to previous studies, we concentrate on the analytical solution rather than using simulation. We investigate how changes in the system parameters affect to some important behavioral indicators of the spread of the pathogen. We also present an exact measure of the number of secondary cases of infection produced by one colonized patient.

A data-driven mathematical model of CA-MRSA transmission among age groups: evaluating the effect of control interventions

Community associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has become a major cause of skin and soft tissue infections (SSTIs) in the US. We developed an age-structured compartmental model to study the spread of CA-MRSA at the population level and assess the effect of control intervention strategies. We used Monte-Carlo Markov Chain (MCMC) techniques to parameterize our model using monthly time series data on SSTIs incidence in children (≤ 19 years) during January 2004 -December 2006 in Maricopa County, Arizona. Our model-based forecast for the period January 2007-December 2008 also provided a good fit to data. We also carried out an uncertainty and sensitivity analysis on the control reproduction number, Rc which we estimated at 1.3 (95% CI [1.2,1.4]) based on the model fit to data. Using our calibrated model, we evaluated the effect of typical intervention strategies namely reducing the contact rate of infected individuals owing to awareness of infection and decolonization strategies targeting symptomatic infected individuals on both [Formula: see text] and the long-term disease dynamics. We also evaluated the impact of hypothetical decolonization strategies targeting asymptomatic colonized individuals. We found that strategies focused on infected individuals were not capable of achieving disease control when implemented alone or in combination. In contrast, our results suggest that decolonization strategies targeting the pediatric population colonized with CA-MRSA have the potential of achieving disease elimination.

Clinical significance of methicillin-resistant Staphylococcus aureus colonization on hospital admission: one-year infection risk

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among inpatients is a well-established risk factor for MRSA infection during the same hospitalization, but the long-term risk of MRSA infection is uncertain. We performed a retrospective cohort study to determine the one-year risk of MRSA infection among inpatients with MRSA-positive nasal polymerase chain reaction (PCR) tests confirmed by positive nasal culture (Group 1), patients with positive nasal PCR but negative nasal culture (Group 2), and patients with negative nasal PCR (Group 3).

METHODOLOGY/PRINCIPAL FINDINGS

Subjects were adults admitted to a four-hospital system between November 1, 2006 and March 31, 2011, comprising 195,255 admissions. Patients underwent nasal swab for MRSA PCR upon admission; if positive, nasal culture for MRSA was performed; if recovered, MRSA was tested for Panton-Valentine Leukocidin (PVL). Outcomes included MRSA-positive clinical culture and skin and soft tissue infection (SSTI). Group 1 patients had a one-year risk of MRSA-positive clinical culture of 8.0% compared with 3.0% for Group 2 patients, and 0.6% for Group 3 patients (p<0.001). In a multivariable model, the hazard ratios for future MRSA-positive clinical culture were 6.52 (95% CI, 5.57 to 7.64) for Group 1 and 3.40 (95% CI, 2.70 to 4.27) for Group 2, compared with Group 3 (p<0.0001). History of MRSA and concurrent MRSA-positive clinical culture were significant risk factors for future MRSA-positive clinical culture. Group 1 patients colonized with PVL-positive MRSA had a one-year risk of MRSA-positive clinical culture of 10.1%, and a one-year risk of MRSA-positive clinical culture or SSTI diagnosis of 21.7%, compared with risks of 7.1% and 12.5%, respectively, for patients colonized with PVL-negative MRSA (p = 0.04, p = 0.005, respectively).

CONCLUSIONS/SIGNIFICANCE

MRSA nasal colonization is a significant risk factor for future MRSA infection; more so if detected by culture than PCR. Colonization with PVL-positive MRSA is associated with greater risk than PVL-negative MRSA.

Infection control strategies for preventing the transmission of meticillin-resistant Staphylococcus aureus (MRSA) in nursing homes for older people

BACKGROUND

Nursing homes for older people provide an environment likely to promote the acquisition and spread of meticillin-resistant Staphylococcus aureus (MRSA), putting residents at increased risk of colonisation and infection. It is recognised that infection prevention and control strategies are important in preventing and controlling MRSA transmission.

OBJECTIVES

To determine the effects of infection prevention and control strategies for preventing the transmission of MRSA in nursing homes for older people.

SEARCH METHODS

In August 2013, for this third update, we searched the Cochrane Wounds Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library), Database of Abstracts of Reviews of Effects (DARE, The Cochrane Library), Ovid MEDLINE, OVID MEDLINE (In-process and Other Non-Indexed Citations), Ovid EMBASE, EBSCO CINAHL, Web of Science and the Health Technology Assessment (HTA) website. Research in progress was sought through Current Clinical Trials, Gateway to Reseach, and HSRProj (Health Services Research Projects in Progress).

SELECTION CRITERIA

All randomised and controlled clinical trials, controlled before and after studies and interrupted time series studies of infection prevention and control interventions in nursing homes for older people were eligible for inclusion.

DATA COLLECTION AND ANALYSIS

Two review authors independently reviewed the results of the searches. Another review author appraised identified papers and undertook data extraction which was checked by a second review author.

MAIN RESULTS

For this third update only one study was identified, therefore it was not possible to undertake a meta-analysis. A cluster randomised controlled trial in 32 nursing homes evaluated the effect of an infection control education and training programme on MRSA prevalence. The primary outcome was MRSA prevalence in residents and staff, and a change in infection control audit scores which measured adherence to infection control standards. At the end of the 12 month study, there was no change in MRSA prevalence between intervention and control sites, while mean infection control audit scores were significantly higher in the intervention homes compared with control homes.

AUTHORS' CONCLUSIONS

There is a lack of research evaluating the effects on MRSA transmission of infection prevention and control strategies in nursing homes. Rigorous studies should be conducted in nursing homes, involving residents and staff to test interventions that have been specifically designed for this unique environment.

Estimating potential infection transmission routes in hospital wards using wearable proximity sensors

Background

Contacts between patients, patients and health care workers (HCWs) and among HCWs represent one of the important routes of transmission of hospital-acquired infections (HAI). A detailed description and quantification of contacts in hospitals provides key information for HAIs epidemiology and for the design and validation of control measures.

Methods and Findings

We used wearable sensors to detect close-range interactions (“contacts”) between individuals in the geriatric unit of a university hospital. Contact events were measured with a spatial resolution of about 1.5 meters and a temporal resolution of 20 seconds. The study included 46 HCWs and 29 patients and lasted for 4 days and 4 nights. 14,037 contacts were recorded overall, 94.1% of which during daytime. The number and duration of contacts varied between mornings, afternoons and nights, and contact matrices describing the mixing patterns between HCW and patients were built for each time period. Contact patterns were qualitatively similar from one day to the next. 38% of the contacts occurred between pairs of HCWs and 6 HCWs accounted for 42% of all the contacts including at least one patient, suggesting a population of individuals who could potentially act as super-spreaders.

Conclusions

Wearable sensors represent a novel tool for the measurement of contact patterns in hospitals. The collected data can provide information on important aspects that impact the spreading patterns of infectious diseases, such as the strong heterogeneity of contact numbers and durations across individuals, the variability in the number of contacts during a day, and the fraction of repeated contacts across days. This variability is however associated with a marked statistical stability of contact and mixing patterns across days. Our results highlight the need for such measurement efforts in order to correctly inform mathematical models of HAIs and use them to inform the design and evaluation of prevention strategies.

Methicillin-resistant staphylococci: implications for our food supply?

Food-borne intoxication, caused by heat-stable enterotoxins produced by Staphylococcus aureus, causes over 240,000 cases of food-borne illness in the United States annually. Other staphylococci commonly associated with animals may also produce these enterotoxins. Foods may be contaminated by infected food handlers during slaughter and processing of livestock or by cross-contamination during food preparation. S. aureus also causes a variety of mild to severe skin and soft tissue infections in humans and other animals. Antibiotic resistance is common in staphylococci. Hospital-associated (HA) S. aureus are resistant to numerous antibiotics, with methicillin-resistant S. aureus (MRSA) presenting significant challenges in health care facilities for over 40 years. During the mid-1990s new human MRSA strains developed outside of hospitals and were termed community-associated (CA). A few years later, MRSA was isolated from horses and methicillin resistance was detected in Staphylococcus intermedius/pseudintermedius from dogs and cats. In 2003, a livestock-associated (LA) MRSA strain was first detected in swine. These methicillin-resistant staphylococci pose additional food safety and occupational health concerns. MRSA has been detected in a small percentage of retail meat and raw milk samples indicating a potential risk for food-borne transmission of MRSA. Persons working with animals or handling meat products may be at increased risk for antibiotic-resistant infections. This review discusses the scope of the problem of methicillin-resistant staphylococci and some strategies for control of these bacteria and prevention of illness.

The importance of nursing homes in the spread of methicillin-resistant Staphylococcus aureus (MRSA) among hospitals

BACKGROUND

Hospital infection control strategies and programs may not consider control of methicillin-resistant Staphylococcus aureus (MRSA) in nursing homes in a county.

METHODS

Using our Regional Healthcare Ecosystem Analyst, we augmented our existing agent-based model of all hospitals in Orange County (OC), California, by adding all nursing homes and then simulated MRSA outbreaks in various health care facilities.

RESULTS

The addition of nursing homes substantially changed MRSA transmission dynamics throughout the county. The presence of nursing homes substantially potentiated the effects of hospital outbreaks on other hospitals, leading to an average 46.2% (range, 3.3%-156.1%) relative increase above and beyond the impact when only hospitals are included for an outbreak in OC's largest hospital. An outbreak in the largest hospital affected all other hospitals (average 2.1% relative prevalence increase) and the majority (~90%) of nursing homes (average 3.2% relative increase) after 6 months. An outbreak in the largest nursing home had effects on multiple OC hospitals, increasing MRSA prevalence in directly connected hospitals by an average 0.3% and in hospitals not directly connected through patient transfers by an average 0.1% after 6 months. A nursing home outbreak also had some effect on MRSA prevalence in other nursing homes.

CONCLUSIONS

Nursing homes, even those not connected by direct patient transfers, may be a vital component of a hospital's infection control strategy. To achieve effective control, a hospital may want to better understand how regional nursing homes and hospitals are connected through both direct and indirect (with intervening stays at home) patient sharing.

Modeling methicillin-resistant Staphylococcus aureus in hospitals: transmission dynamics, antibiotic usage and its history

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) is endemic in many hospital settings, posing substantial threats and economic burdens worldwide.

METHODS

We propose mathematical models to investigate the transmission dynamics of MRSA and determine factors that influence the prevalence of MRSA infection when antibiotics are given to patients to treat or prevent infections with either MRSA itself or other bacterial pathogens.

RESULTS

Our results suggest that: (i) MRSA always persists in the hospital when colonized and infected patients are admitted; (ii) the longer the duration of treatment of infected patients and the lower the probability of successful treatment will increase the prevalence of MRSA infection; (iii) the longer the duration of contamination of health care workers (HCWs) and the more their contacts with patients may increase the prevalence of MRSA infection; (iv) possible ways to control the prevalence of MRSA infection include treating patients with antibiotic history as quickly and efficiently as possible, screening and isolating colonized and infected patients at admission, and compliance with strict hand-washing rules by HCWs.

CONCLUSION

Our modeling studies offer an approach to investigating MRSA infection in hospital settings and the impact of antibiotic history on the incidence of infection. Our findings suggest important influences on the prevalence of MRSA infection which may be useful in designing control policies.