Nasal carriage of Staphylococcus aureus in Australian (pre-clinical and clinical) medical students

Prevalence of Staphylococcus aureus Nasal Carriage and Methicillin-resistant S. aureus Among Medical Students: A Systematic Review and Meta-analysis

Context: Evaluating the prevalence of Staphylococcus aureus nasal carriage and methicillin-resistant S. aureus (MRSA) that are sources of nosocomial infection among medical students. Evidence Acquisition: Electronic databases were searched by preferred subject headings and free-text keywords. After omitting duplicates, retrieved articles were screened by two independent reviewers in a three-step process based on inclusion criteria. Then, reviewers critically appraised the selected studies by JBI checklists and extracted the required data. Finally, the pooled prevalence rates of S. aureus nasal carriage and MRSA were meta-analyzed by Stata V.16 software. The heterogeneity of included studies was calculated by I2 and chi-square. Subgroup analysis was carried out according to study designs, as well as the continent origin of clinical and preclinical students. Results: Of 858 retrieved studies, 15 were included in the meta-analysis. The results showed that the pooled prevalence of nasal S. aureus carriage was 28% [prevalence rate: 0.028, 95% CI: 0.21 - 0.34, P < 0.001, I2: 96.40%, chi2: 360.98 (df = 14)]. The prevalence of S. aureus among clinical students was 33% (pooled prevalence rate: 0.33, 95% CI: 0.18 - 0.47) whereas, in preclinical students, it was 25% (pooled prevalence rate: 0.25, 95% CI: 0.23 - 0.28). Also, in a subgroup analysis of continents, Australia (Oceania) had the highest prevalence rate. According to an evaluation of publication bias, the distribution of studies was very high. Moreover, pooled MRSA prevalence among medical students was 2% (prevalence rate: 0.02 95% CI: 0.01 - 0.03, P < 0.001). Conclusions: In this meta-analysis, S. aureus and MRSA prevalence rates among medical students were estimated at 28% and 2%, respectively. More attention should be given to the prevention of MRSA colonization and screening strategies among medical students across the world.

Incidence of community onset MRSA in Australia: least reported where it is Most prevalent

Background

This is the first review of literature and synthesis of data on community onset methicillin resistant Staphylococcus aureus (CO-MRSA) infections in Australia. Incidence of CO-MRSA varies considerably in Australia, depending on geographic and demographic factors.

Methods

Data for the rates of MRSA infections were collected from articles identified using PubMed, Scopus, the grey literature and data from State and Federal Government Surveillance Systems. We synthesized data and developed a framework for how data was selected, collated, linked, organized and interpreted.

Results

The results of our literature search demonstrates considerable gaps in the reporting of CO-MRSA in Australia. Consequently, total incidences were under reported; however the available data suggests the incidence varied between 44 (Tasmania) and 388 (southern Northern Territory) cases per 100,000 person years. Hospitalised cases of CO-MRSA varied between 3.8 (regional Victoria) and 329 (southern Northern Territory). Taking the median percentage of infections by site for all regions available, skin and soft tissue infections (SSTIs) consisted of 56% of hospitalized CO-MRSA, compared with bacteremias, which represented 14%. No region had a complete data set of CO-MRSA infections treated in out-patient settings and so incidences were underestimates. Nevertheless, estimates of the incidence of CO-MRSA treated outside hospitals varied between 11.3 (Melbourne) and 285 (Northern Territory) per 100,000 person-years. These infections were chiefly SSTIs, although urinary tract infections were also noted.Incidences of CO-MRSA blood-stream infections and outpatient skin and soft tissue infections have been increasing with time, except in Tasmania. CO-MRSA is observed to affect people living in remote areas and areas of socioeconomic disadvantage disproportionately.

Conclusions

We generated the first estimates of the incidence of CO-MRSA infections in Australia and identified stark regional differences in the nature and frequency of infections. Critically, we demonstrate that there has been a lack of consistency in reporting CO-MRSA and a general dearth of data. The only government in Australia that requires reporting of CO-MRSA is the Tasmanian, where the infection was least prevalent. Some regions of Australia have very high incidences of CO-MRSA. To improve surveillance and inform effective interventions, we recommend a standardized national reporting system in Australia that reports infections at a range of infection sites, has broad geographic coverage and consistent use of terminology. We have identified limitations in the available data that hinder understanding the prevalence of CO-MRSA.

Sinus bacteriology in patients with cystic fibrosis or primary ciliary dyskinesia: A systematic review

BACKGROUND

A correlation exists between the microbial flora of the upper and lower airways in patients with cystic fibrosis (CF) or with primary ciliary dyskinesia (PCD). The sinuses can function as a bacterial reservoir where gram-negative bacteria adapt to the airways and repeatedly are aspirated to and colonize the lungs according to the theory of the united (unified) airways. Whereas the pattern of bacterial flora in the lower airways has been extensively studied, the upper airways have drawn limited attention.

OBJECTIVE

Our aim was to review the literature that reported bacterial flora in the sinuses and nasal cavities of patients with CF or PCD.

METHODS

A number of medical literature data bases were systematically searched between January 1960 and July 2016. We applied the following inclusion criteria: a minimum of one case of PCD (or Kartagener syndrome) or CF, and microbiology analyses from the nose or paranasal sinuses.

RESULTS

We included 46 studies (1823 patients) from 16 countries. Staphylococcus aureus was found in 30% of the noses and sinuses of patients with CF. Other common bacteria found included Pseudomonas aeruginosa, coagulase negative staphylococci, and Haemophilus influenzae. In PCD, H. influenzae was the most common bacteria (28%), followed by Streptococcus pneumoniae and P. aeruginosa. If studies that included nonsurgical swab and blowing samples were excluded, then P. aeruginosa was the most common bacterium in patients with CF (34%) and in patients with PCD (50%), followed by S. aureus and H. influenza.

CONCLUSION

S. aureus, P. aeruginosa, coagulase negative staphylococci, and H. influenzae dominated in the upper airways of patients with CF. In patients with PCD, H. influenzae, S. pneumoniae, and P. aeruginosa dominated. When studies that included swab and blowing samples were excluded, P. aeruginosa was the most common bacterium in both groups. Direct comparisons among the studies were restricted due to very heterogeneous methods, and a better standardization of procedures and outcomes is needed.

Hospital clones of methicillin-resistant Staphylococcus aureus are carried by medical students even before healthcare exposure

Background

Methicillin-resistant Staphylococcus aureus (MRSA) strains are prevalent in healthcare and the community. Few studies have examined MRSA carriage among medical students.

The aim of this study is to examine Staphylococcus aureus (SA) carriage, and particular MRSA, over time in cohort medical students

Methods

Prospective collection of nasal swabs from medical students in Israel and assessment of SA carriage. Three samples were taken per student in preclinical and clinical parts of studies. Antibiotic susceptibilities were recorded and MRSA typing was performed by staphylococcal cassette chromosome mec (SCCmec) types, Panton Valentine Leukocidin (PVL) encoding genes, and spa types. Clonality was assessed by pulsed-field gel electrophoresis.

Results

Among 58 students, SA carriage rates increased from 33% to 38% to 41% at baseline (preclinical studies), 13 and 19 months (clinical studies), respectively (p = 0.07). Methicillin-susceptible SA (MSSA) carriage increased in the clinical studies period (22 to 41%, p = 0.01). Overall, seven students (12%) carried 13 MRSA isolates. MRSA isolates were PVL negative and were characterized as SCCmecII-t002, SCCmecIV-t032, or t12435 with untypable SCCmec. MRSA carriage during the pre-clinical studies was evident in 4/7 students. Two students carried different MRSA clones at various times and persistent MRSA carriage was noted in one student. Simultaneous carriage of MRSA and MSSA was not detected.

Conclusions

MSSA carriage increased during the clinical part of studies in Israeli medical students. Compared with previous reports, higher rates of MRSA carriage were evident. MRSA strains were genotypically similar to Israeli healthcare-associated clones; however, carriage occurred largely before healthcare exposure, implying community-acquisition of hospital strains.

Prevalence and antimicrobial susceptibility profiles of Staphylococcus aureus nasal carriage among pre-clinical and clinical medical students in a Tanzanian University

Background

Methicillin resistant Staphylococcus aureus (MRSA) nasal carriage is a potential niche for spread and a risk factor for subsequent infections. Despite the fact that medical students are exposed to patients in the hospital during their training, information on S. aureus and MRSA nasal carriage among medical students in Tanzania remains to be dearth so as to guide appropriate infection control and preventive measures.

Methods

A cross-sectional study involving 314 medical students, pre-clinical (n = 166) and clinical (n = 148), at Catholic University of Health and Allied Sciences (CUHAS) was conducted from February to June 2013. Nasal swabs from eligible students were taken and processed using standard operating procedures so as to identify S. aureus, MRSA and their respective antimicrobial susceptibility patterns.

Results

The median age (interquartile range) of the study participants was 24 (22–27) years with approximately 69.4 % being males. S. aureus accounted for 21.0 % (66/314) of which 1.5 % (1/66) was MRSA; giving an overall MRSA nasal carriage prevalence of 0.3 % (1/314). Staphylococcus aureus carriage among pre-clinical and clinical students were 19.9 % (33/166) and 22.3 % (33/148) respectively. MRSA carriage was found in one preclinical student with history of working in hospital for years prior to join CUHAS. Staphylococcus aureus carriage was significantly more in older median age group among clinical students compared to preclinical students (p < 0.001). Majority of the isolates were resistant to Ampicillin (87.9 %, 58/66) while all were sensitive to Ciprofloxacin and Vancomycin.

Conclusion

There is high prevalence of S. aureus carriage among medical students at CUHAS. Fortunately, MRSA was found in only one student. In the light of these findings, focused MRSA surveillance to other potential sources like health care workers, patients and environment should be carried out in this setting.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-016-1858-0) contains supplementary material, which is available to authorized users.

Low methicillin-resistant Staphylococcus aureus carriage rate among Italian dental students

We assessed methicillin-resistant Staphylococcus aureus (MRSA) carriage rate among dental students from an Italian university. A total of 157 subjects participated (67 preclinical students and 90 clinical students); samples were collected from the nose, mouth, and skin. Five preclinical students and 0 clinical students were MRSA-positive. Carriage rates were 3.2% (95% confidence interval [CI], 0.4%-6.0%) overall, 7.5% (95% CI, 1.2%-13.8%) in preclinical students and 0% in clinical students. There were 2 MRSA clusters among the preclinical students: 3 second-year and 2 first-year students, who sat close to one another in the classroom the day of the sample. MRSA carriage was not associated with dental health care. The pooled carriage rate among dental students was assessed to obtain a reliable figure of carriage rate unaffected by local conditions. The 4 published surveys were pooled, and the fixed-effects method was used. Among the 484 dental students, the pooled carriage rate was 4.1% (95% CI, 2.4%-5.8%).

Prevalence, risk factors and sequelae of Staphylococcus aureus carriage in diabetes: the Fremantle Diabetes Study Phase II

AIMS

To determine the prevalence and associates of Staphylococcus aureus and methicillin-resistant S. aureus (MRSA) carriage in community-based diabetes, and their relationship to hospitalization with S. aureus infection.

METHODS

A cross-sectional subset of 660 Fremantle Diabetes Study Phase II patients (mean±SD age 65.1±11.5years, 53.1% males) had nasal/axillary swabs as part of biennial review. Serum 25-hydroxyvitamin D (25(OH)D) concentrations were measured in 358 patients. Those with positive swabs were invited back for a repeat swab. Hospitalizations with S. aureus infections were ascertained from validated data linkage. Multiple logistic regression was used to identify associates of carriage, and Cox proportional hazards modelling was used to determine predictors of subsequent hospitalization.

RESULTS

258 patients (39.1%) were positive for S. aureus and eight (3.1%) carried MRSA. S. aureus carriage was independently associated with being married/in a de facto relationship and inversely with older age and being born overseas (P≤0.043). Repeat swabs in 137 patients (53.1% of those with an initially positive swab) grew S. aureus in 113 (82.5%). Five of eight MRSA-positive patients were re-swabbed, and four were MRSA-positive. Independent predictors of hospitalization with staphylococcal infection after the initial swab were S. aureus carriage (hazard ratio (95% CI) 5.42 (1.49-19.79)), prior hospitalization with S. aureus (4.84 (1.19-19.63)) and Aboriginality (7.20 (1.91-27.17) (P≤0.027). Serum 25(OH)D was not associated with S. aureus carriage or subsequent hospitalization.

CONCLUSIONS

S. aureus and MRSA carriage in our patients was consistent with previous general population studies. There were no diabetes-specific risk factors. Persistent colonization may underlie the increased risk of hospitalization with S. aureus.

Methicillin-resistant Staphylococcus aureus colonization among medical residents

BACKGROUND

Medical residents may be at risk of becoming colonized by methicillin-resistant Staphylococcus aureus (MRSA) during their training. The occupational risk of this specific population is unknown. Furthermore, there are no data regarding MRSA colonization among health care professionals in Quebec.

OBJECTIVE

To determine the MRSA colonization rate in Laval University (Quebec City, Quebec) medical residents and compare it with the MRSA colonization rate of a control group.

METHODS

A controlled cross-sectional study of MRSA prevalence among medical residents of Laval University was performed. The control group consisted of Laval University undergraduate medical students without previous clinical rotations in their curriculum. After informed consent was obtained, participants were screened for MRSA with a nasal swab in both anterior nares. They also completed a questionnaire regarding relevant risk factors and demographic data.

RESULTS

A total of 250 residents of all residency levels from medical and surgical specialties and 247 controls were recruited between February and April 2010. One case of MRSA colonization was detected among the residents and none in the control group (prevalence of 0.4% versus 0.0%; P=1.00).

DISCUSSION

MRSA nasal carriage was very low among Laval University residents. This may reflect the decreasing rate of health care-associated MRSA in Quebec City. Young age and good health may also explain this low risk. The strict infection control policies for MRSA patients (including cohorting, use of gloves, gown and patient-dedicated equipment) may also contribute to prevent MRSA transmission.

CONCLUSIONS

Medical residents in Quebec City appeared to be at very low risk of contracting MRSA through professional activities.

Molecular identification and antimicrobial susceptibility of Staphylococcus aureus nasal isolates from medical students in Cartagena, Colombia

Staphylococcus aureus (SA) remains a major cause of nosocomial and community-acquired infections worldwide. Nasal carriage of this bacterium among hospital personnel constitutes an important source for nosocomial infections. A cross-sectional study enrolling the whole medical student population (n=387) of the School of Medicine at the Universidad de Cartagena, Colombia, was conducted to evaluate the carriage rates of both methicillin sensitive- and methicillin resistant-SA, the frequency of Panton-Valentine leukocidin genes in the isolates, and risk factors associated with carriage in this selected population. After signing an informed consent, participants completed a survey related to possible risk factors for colonization, and nasal swabs were collected from anterior nares. Staphylococcus aureus strains isolated from carriers were subjected to DNA extraction and PCR assays to determine the presence of MecA and Panton-Valentine leukocidin genes. Typing of the staphylococcal chromosomal cassette was performed for methicillin resistant strains. Molecular analysis was performed for only one strain per carrier. Prevalence of carriage for methicillin sensitive- and methicillin resistant-SA was 25% and 1.6% respectively. Most of the methicillin resistant isolates carried the staphylococcal chromosomal cassette type IV and the genes for Panton-Valentine leukocidin. To determine carrier types among medical students, each participant was subjected to four additional swabs, each taken two weeks apart. 9.8% persistent carriers, 53.1% intermittent carriers, and 37.1% non-carriers of SA were found. There was no association between risk factors analyzed and carriage of the bacterium. The study was conducted from April to September 2009 and found a persistent carriage of methicillin resistant-SA strains bearing the genes for Panton-Valentine leukocidin among medical students, evidencing the potential contribution of this portion of healthcare personnel either to the spread or introduction of these strains into the healthcare environment.

Nasal carriage rate and molecular epidemiology of methicillin-resistant Staphylococcus aureus among medical students at a Taiwanese university

OBJECTIVE

To investigate whether clinical exposure in the hospital affects nasal carriage of methicillin-resistant Staphylococcus aureus (MRSA) among medical students.

METHODS

A total of 322 medical students, both pre-clinical (n=167) and clinical (n=155), were recruited. Specimens were obtained from the nares of the subjects for the detection of S. aureus. A questionnaire was completed for each subject. All the MRSA isolates were further molecularly characterized.

RESULTS

The overall S. aureus carriage rate was 19.3%, with a rate of 16.8% for pre-clinical students and 21.9% for clinical students (p=0.26). The carriage rate of MRSA was 2.2%, with a rate of 2.4% for pre-clinical students and 1.9% for clinical students (p=0.54). There was no significant difference between the pre-clinical and clinical students in terms of nasal carriage of S. aureus and MRSA. All seven MRSA isolates were categorized as community strains in Taiwan. The risk factors for acquisition of S. aureus included male gender, age ≥23 years, and not taking antibiotics in the past year.

CONCLUSIONS

As in the general population, less than 5% of medical students in northern Taiwan harbored MRSA, categorized as community strains, in their nares. The carriage of MRSA was not affected by clinical exposure in the hospital for 1-2 years.

Screening of Staphylococcus aureus nasal strains isolated from medical students for toxin genes

Three hundred twenty-one students (156 students with no clinical exposure and 165 students with clinical exposure) were screened for nasal colonization by Staphylococcus aureus; 20.9% of students were S. aureus nasal carriers, and 40.3% of S. aureus isolates harbored toxin genes. The most prevalent genes were tst (15.0 %) and sec (13.4 %). Isolates with multiple genes were only found among clinical students (p = 0.045). Six of 11 PFGE clones were positive for toxin genes. Methicillin-resistant (MRSA) isolates were only detected in the clinical students (4.5 %). The exposure of students to the hospital environment neither radically increased S. aureus nasal carriage, nor the frequency of clinically important toxin gene presence, but it could have influenced the positive selection of toxigenic MRSA strains.

Health-care workers: source, vector, or victim of MRSA?

There is ongoing controversy about the role of health-care workers in transmission of meticillin-resistant Staphylococcus aureus (MRSA). We did a search of the literature from January, 1980, to March, 2006, to determine the likelihood of MRSA colonisation and infection in health-care workers and to assess their role in MRSA transmission. In 127 investigations, the average MRSA carriage rate among 33 318 screened health-care workers was 4.6%; 5.1% had clinical infections. Risk factors included chronic skin diseases, poor hygiene practices, and having worked in countries with endemic MRSA. Both transiently and persistently colonised health-care workers were responsible for several MRSA clusters. Transmission from personnel to patients was likely in 63 (93%) of 68 studies that undertook genotyping. MRSA eradication was achieved in 449 (88%) of 510 health-care workers. Subclinical infections and colonisation of extranasal sites were associated with persistent carriage. We discuss advantages and disadvantages of screening and eradication policies for MRSA control and give recommendations for the management of colonised health-care workers in different settings.

Nasal carriage of pathogenic bacteria in medical students: effects of clinic exposure on prevalence and antibiotic susceptibility

Staphylococcus aureus is a major cause of community-acquired and nosocomial infections worldwide. One important source of this pathogen for nosocomial infections is the nasal carriage of S. aureus among hospital personnel. There are only a few studies investigating the carriage of S. aureus in a community of medical students. Oral and nasal flora of 179 medical students with varying clinical exposures were determined. Oral cultures revealed no nosocomial pathogen and nasal cultures showed an increasing rate of S. aureus carriage with increasing clinical exposure. Methicillin resistance also demonstrated a tendency toward increasing with increasing clinical exposure.

Staphylococcus aureus nasal carriage in a student community: prevalence, clonal relationships, and risk factors

OBJECTIVE

To evaluate the prevalence and risk factors of nasal Staphylococcus aureus (SA) in the community.

DESIGN

Cross-sectional study.

SETTING

Wake Forest University, Winston-Salem, North Carolina.

PARTICIPANTS

Four hundred fifty students were screened for nasal SA carriage during the fall of 2000, 2001, and 2002.

METHODS

Students were screened by nose swabs. A self-administered questionnaire collected information on demographics and medical history. Antibiotic testing and PFGE were performed on isolates. Risk factors were determined by logistic regression analysis.

RESULTS

Of 450 volunteers, 131 (29%) were SA carriers. Antibiotic resistance was high for azithromycin (26%) and low for ciprofloxacin (1%), tetracycline (5%), mupirocin (1%), and methicillin (2%). PFGE patterns were not associated with carriage. Age, male gender, white race, medical student, allergen injection therapy, chronic sinusitis, rheumatoid arthritis, hospitalization for 6 months or less, and use of antibiotics were associated with carrier status by univariate analysis. Stepwise multivariate logistic regression led to a best fitting model with older age (OR, 1.04; CI95, 1.005-1.079), male gender (OR, 1.50; CI95, 0.982-2.296), and chronic sinusitis (OR, 2.71; CI95, 0.897-8.195) as risk factors. Antibiotic use (< 4 weeks) (OR, 0.41; CI95, 0.152-1.095) and allergen injection therapy (OR, 0.41; CI95, 0.133-1.238) were protective. Analyses of carriers revealed candidate factors for persistent carriage to be nasal SA colonization rate and male gender. Factors for azithromycin resistance were non-medical students and antibiotic use in the past 6 months.

CONCLUSION

Older male volunteers suffering from chronic sinusitis and not taking antibiotics were at higher risk for carrying SA.

Nasal carriage of Staphylococcus aureus: epidemiology, underlying mechanisms, and associated risks

Staphylococcus aureus has long been recognized as an important pathogen in human disease. Due to an increasing number of infections caused by methicillin-resistant S. aureus (MRSA) strains, therapy has become problematic. Therefore, prevention of staphylococcal infections has become more important. Carriage of S. aureus appears to play a key role in the epidemiology and pathogenesis of infection. The ecological niches of S. aureus are the anterior nares. In healthy subjects, over time, three patterns of carriage can be distinguished: about 20% of people are persistent carriers, 60% are intermittent carriers, and approximately 20% almost never carry S. aureus. The molecular basis of the carrier state remains to be elucidated. In patients who repeatedly puncture the skin (e.g., hemodialysis or continuous ambulatory peritoneal dialysis [CAPD] patients and intravenous drug addicts) and patients with human immunodeficiency virus (HIV) infection, increased carriage rates are found. Carriage has been identified as an important risk factor for infection in patients undergoing surgery, those on hemodialysis or CAPD, those with HIV infection and AIDS, those with intravascular devices, and those colonized with MRSA. Elimination of carriage has been found to reduce the infection rates in surgical patients and those on hemodialysis and CAPD. Elimination of carriage appears to be an attractive preventive strategy in patients at risk. Further studies are needed to optimize this strategy and to define the groups at risk.