Nasal Swab Cultures Research Articles

Prevalence of Staphylococcus aureus Colonization in Orthopaedic Surgeons and Their Patients

Methicillin-resistant Staphylococcus aureus and methicillin-sensitive Staphylococcus aureus surgical site infections are an increasing health problem in the United States. To date, no study, as far as we know, has evaluated the prevalence of Staphylococcus aureus colonization in orthopaedic surgeons. The purpose of our study was to assess the prevalence of methicillin-resistant Staphylococcus aureus and methicillin-sensitive Staphylococcus aureus colonization in orthopaedic surgery attending surgeons and residents at our institution compared with that in our high-risk patients.We performed nasal swab cultures in seventy-four orthopaedic attending surgeons and sixty-one orthopaedic surgery residents at our institution, screening for methicillin-resistant Staphylococcus aureus and methicillin-sensitive Staphylococcus aureus. We compared these results with a prospective database of nasal cultures of patients undergoing joint replacement and spine surgery.A total of 135 physicians were screened. Of those physicians, 1.5% were positive for methicillin-resistant Staphylococcus aureus and 35.7% were positive for methicillin-sensitive Staphylococcus aureus. None of the sixty-one residents were positive for methicillin-resistant Staphylococcus aureus. However, 59% were positive for methicillin-sensitive Staphylococcus aureus. Of the seventy-four attending surgeons, 2.7% were positive for methicillin-resistant Staphylococcus aureus and 23.3%, for methicillin-sensitive Staphylococcus aureus. Previous studies at our institution have demonstrated a 2.17% prevalence of nasal carriage of methicillin-resistant Staphylococcus aureus and an 18% rate of methicillin-sensitive Staphylococcus aureus in high-risk patients. Thus, no difference was found between the prevalence of methicillin-resistant Staphylococcus aureus in residents or attending surgeons and that in the high-risk patients. However, the prevalence of methicillin-sensitive Staphylococcus aureus colonization in the surgeons (35.7%) was significantly higher than that in the high-risk patient group (18%) (p < 0.01).At a major teaching hospital, a higher prevalence of methicillin-sensitive Staphylococcus aureus colonization was found among attending and resident orthopaedic surgeons compared with a high-risk patient group, but the prevalence of methicillin-resistant Staphylococcus aureus colonization was similar.

Role of nasal methicillin-resistant Staphylococcus aureus screening in the management of skin and soft tissue infections

We set out to determine whether nasal swab isolates can identify methicillin-resistant Staphylococcus aureus (MRSA) colonization and guide therapy in skin and soft tissue infections (SSTI). Among hospitalized patients admitted to a general medicine service with SSTI, specificity and positive predictive value for MRSA in nasal swab isolates were 100%; sensitivity was 55%. Thus, positive nasal swab cultures may help identify MRSA colonization and guide antimicrobial therapy for SSTI when wound cultures cannot be obtained.

Perioperative management of neurosurgical patients with methicillin-resistant Staphylococcus aureus

The emergence of methicillin-resistant Staphylococcus aureus (MRSA) has posed a challenge in the treatment of neurosurgical patients. The authors investigated the impact of MRSA colonization and infection in the neurosurgical population at a community-based, tertiary care referral center. Hospitalized patients under the care of the Kaiser Permanente inpatient neurosurgery service were prospectively entered into a database. In Phase I of the study, 492 consecutive patients were followed. Per hospital policy, the 260 patients from this group who were admitted to the intensive care unit (ICU) underwent screening for MRSA based on nasal swab cultures and a review of their medical history for prior MRSA infections. These patients were designated as either MRSA positive (17 patients, 6.5% of screened patients) or MRSA negative (243 patients). The 232 patients admitted to non-ICU nursing units did not undergo MRSA screening and were designated as unscreened. In Phase II of the study, the authors reviewed 1005 neurosurgical admissions and completed a detailed chart review in 62 MRSA-positive patients (6.2%). Eleven patients received nonoperative treatment. Five patients presented with community-acquired neurosurgical infections, and the causative organism was MRSA in 3 cases. Forty-six patients underwent 55 procedures, and the authors reviewed their perioperative management. In Phase I of the study, the authors found that for the MRSA-positive, MRSA-negative, and unscreened groups, the rates of postoperative neurosurgical wound infections caused by all pathogens were 23.5, 4.1, and 1.3%, respectively. For MRSA wound infections, the rates were 23.5, 0.8, and 0%, respectively. In Phase II, patients with MRSA were noted to have the following clinical features: male sex in 63%, a malignancy in 39.1%, diabetes in 34.8%, prior MRSA infection in 21.7%, immunosuppressed state in 17.4%, and a traumatic injury in 15.2%. The rate of postoperative neurosurgical wound infection in patients who received MRSA-specific prophylactic antibiotic therapy (usually vancomycin) was 7.4% (27 procedures) compared with 32.1% (28 procedures) in patients who received the standard treatment (usually cefazolin) (p = 0.04). Wound care for ICU patients was standardized for postoperative Days 0-7 with chlorhexidine cleaning at bandage changes at 3-day intervals. Wound cultures from neurosurgical site infections in patients with prior MRSA colonization or infection grew MRSA in 7 of 11 patients. Neurosurgical patients identified with MRSA colonization or a prior history of MRSA infections benefit from specific perioperative care, including prophylactic antibiotics active against MRSA (such as vancomycin) and postoperative wound care with coverings and chlorhexidine antisepsis to reduce MRSA wound colonization.

Dépistage systématique du portage nasal du Staphyloccocus aureus résistant à la méticilline (SARM) chez les patients hospitalisés en dermatologie : expérience de l’hôpital Saint-Louis

In a bid to combat methicillin-resistant Staphylococcus aureus (MRSA) more efficiently in our department, we performed a study to 1) clarify the MRSA carriage rate in patients hospitalized in the department; 2) evaluate the rate of MRSA acquisition during hospitalization; 3) describe the MRSA carrier profile; 4) study the morbidity and mortality associated with MRSA.We conducted a three-month prospective study in all patients hospitalized for more than 24hours in the dermatology department of the Saint-Louis Hospital. Nasal swab cultures were performed on the day of admission, once a week thereafter and on the day of discharge. Clinical and epidemiological data were individually reviewed by means of a standardized questionnaire.In 310 patients, the prevalence of nasal MRSA carriage at admission was 6.5%. During hospitalization, 1.9% of our patients became colonized with MRSA. MRSA carriers were significantly older than non-carriers and had been hospitalized more frequently over the previous 12 months, principally in intensive care or in intermediate or long-term care facilities, and erosive and/or ulcerated dermatitis was more common in this population. Of the 27 patients colonized with MRSA, only three had MRSA infections, and these were successfully treated with antibiotics.The observed rate of MRSA carriage was close to that seen in intensive care units (7%). While systematic screening for MRSA in patients with erosive and/or ulcerated dermatitis would allow detection of twice as many cases of MRSA than the usual screening recommendations, this would be associated with little tangible benefit and high costs, and we therefore decided not to change the usual MRSA screening politic in our dermatology department.

S294 – Pre-op Prevalence of MRSA in Intranasal Surgery Patients

Objectives 1) Understand the extent of methicillin-resistant Staphylococcus aureus among those undergoing intranasal surgery. 2) Be able to describe potential risk factors for MRSA colonization. The purpose of this study is to outline a prevalance of MRSA colonization among those undergoing inranasal surgery, with an exploration of potential risk factors for colonization. Methods Patients undergoing intranasal surgery (endoscopic sinus surgery, rhinoplasty, septoplasty, etc) at a tertiary care medical center had preoperative nasal swab cultures. The primary endpoint was positive culture of methicillin-resistant Staphylococcus aureus (MRSA). Patient demographic information was also collected to ascertain potential risk factors for colonization of MRSA. Results Early results have demonstrated that the prevalence of MRSA in patients is less than the reported prevalence in hospital inpatient populations. Of the initial 25 patients enrolled in this study, none were shown to be colonized with methicillin-resistant Staphylococcus aureus (0/25), with 1 patient having reported a history of MRSA infection (4%). Conclusions Preliminary data suggests that the prevalence of methicillin-resistant Staphylococcus aureus among patients undergoing intranasal surgery is less than the prevalence of inpatient populations as reported in several previous studies. While preliminary data suggests a potential decreased prevalence of MRSA in this population, a much larger sample of patients is needed to make a more definitive statement. In the coming weeks and months, as more data is gathered and the sample size included in the study grows, it will be interesting to note whether the initial trend, as suggested here, continues.

A Preoperative Decolonization Protocol for Staphylococcus aureus Prevents Orthopaedic Infections

Staphylococcus aureus (S. aureus) is an independent risk factor for orthopaedic surgical site infection (SSI). To determine whether a preoperative decolonization protocol reduces S. aureus SSIs, we conducted a prospective observational study of patients undergoing elective total joint arthroplasty (TJA) at our institution, with two control groups. The concurrent control group comprised patients of surgeons who did not participate in the intervention study. The preintervention control group comprised patients of participating surgeons who had undergone elective TJA during the year before the study. Patients in the intervention group were screened preoperatively for S. aureus by nasal swab cultures. S. aureus carriers were decolonized with mupirocin ointment to the nares twice daily and chlorhexidine bath once daily for 5 days before surgery. All 164 of 636 participants (26%) who tested positive completed the decolonization protocol without adverse events and had no postoperative S. aureus SSIs at 1-year followup. In contrast, 1330 concurrent control patients had 12 S. aureus infections. If these infections had occurred in the 26% of patients expected to be nasal carriers of S. aureus at a given time, the infection rate would have been 3.5% (12 of 345) in the control group. In addition, the overall infection rate of the participating surgeons, including nonstaphylococcal infections, decreased from 2.6% during the preintervention period to 1.5% during the intervention period, translating to an adjusted economic gain of $231,741 for the hospital. The data suggest a preoperative decolonization protocol reduces S. aureus SSIs in patients undergoing TJA. Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Importance of Bacterial Burden Among Methicillin-Resistant Staphylococcus aureus Carriers in a Long-Term Care Facility

To evaluate the prevalence and transmission of methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization, as well as risk factors associated with MRSA carriage, among residents of a long-term care facility (LTCF). Prospective, longitudinal cohort study. A 100-bed Veterans Administration LTCF. All current and newly admitted residents of the LTCF during an 8-week study period. Nasal swab samples were obtained weekly and cultured on MRSA-selective media, and the cultures were graded for growth on a semiquantitative scale from 0 (no growth) to 6 (heavy growth). Epidemiologic data for the periods before and during the study were collected to assess risk factors for MRSA carriage. Of 83 LTCF residents, 49 (59%) had 1 or more nasal swab cultures that were positive for MRSA; 34 (41%) were consistently culture-negative (designated "noncarriers"). Of the 49 culture-positive residents, 30 (36% of the total of 83 residents) had all cultures positive for MRSA (designated "persistent carriers"), and 19 (23% of the 83 residents) had at least 1 culture, but not all cultures, positive for MRSA (designated "intermittent carriers"). Multivariate analysis showed that participants with at least 1 nasal swab culture positive for MRSA were likely to have had previous hospitalization (odds ratio, 3.9) or wounds (odds ratio, 8.2). Persistent carriers and intermittent carriers did not differ in epidemiologic characteristics but did differ in mean MRSA growth score (3.7 vs 0.7; P<.001). Epidemiologic characteristics differed between noncarriers and subjects with at least 1 nasal swab culture positive for MRSA. However, in this LTCF population, only the degree of bacterial colonization (as reflected by mean MRSA growth score) distinguished persistent carriers from intermittent carriers. Understanding the burden of colonization may be important when determining future surveillance and control strategies.

Identification of Methicillin Resistant Staphylococcus aureus (MRSA) and Methicillin Resistant Coagulase-Negative Staphylococcus (CoNS) in Clinical Settings

To evaluate different methods for the identification of methicillin-resistant Staphylococci and their reliability, 112 Staphylococcal isolates (32 Staphylococcus aureus isolates and 80 coagulase negative Staphylococci isolates “CoNS”) were collected from 118 nasal swab cultures and were subjected to three methods to detect oxacillin susceptibility of the isolates. The three methods were oxacillin disk diffusion method; the Epsilometer- test (E-test) and polymerase chain reaction (PCR). For the S. aureus strains, the E-test and the PCR methods showed discrepant results in two isolates (6.25%); that showed susceptible patterns with the E-test, but were resistant by the disk diffusion method. Both isolates were negative for the presence of mecA gene. Seven (8.75%) out of the 80 CoNS isolates showed conflicting results where four isolates showed resistance with the disk diffusion and the E-test methods, and had negative mecA gene by PCR. Three of the 7 CoNS with the conflicting results showed a susceptible pattern to oxacillin by the E-test method, while the PCR method showed the presence of mecA gene. We concluded that combination of molecular and conventional methods should be used to assess methicillin resistance of Staphylococci in clinical practices.

Host–microbe interplay in persistent Staphylococcus aureus nasal carriage in HIV patients

It has been shown that persistent Staphylococcus aureus nasal carriage results in increased bacterial dispersal and a higher risk of infection compared to non-or-intermittent S. aureus carriage. Although many studies investigated S. aureus nasal carriage in HIV patients, none compared persistent carriage to non-persistent carriage nor were studies performed in the HAART era. We investigated the host–microbe interplay of persistent S. aureus nasal carriage in HIV-infected patients by studying host determinants of persistent carriage as well as the genetic structure of S. aureus strains isolated. We compared this genetic structure with the previously determined population structure of S. aureus isolates obtained from healthy individuals. Between February 2004 and June 2005 all HIV patients visiting the outpatient department of Erasmus MC (Rotterdam, The Netherlands) were asked to participate in this study. Participants were interviewed and screened for persistent S. aureus carriage using two semi-quantitative nasal swab cultures. For 443 patients two cultures were available, 131 (29.6%) were persistent carriers, which is significantly higher as compared to healthy individuals from the same geographic region (17.6%; P < 0.0001). Male sex (odds ratio [OR], 2.22; 95% confidence interval [CI], 1.32–3.73), current smoking (OR, 0.58; 95% CI, 0.38–0.90), Pneumocystis jiroveci pneumonia (PCP) prophylaxis (OR, 0.39; 95% CI, 0.16–0.97) and antiretroviral therapy (OR, 0.61; 95% CI, 0.38–0.98) were independent determinants of persistent carriage. Only two strains were mecA positive (1.2%) and no PVL positive strains were detected. The population structure of S. aureus strains isolated from HIV patients appeared to be strongly overlapping with that of S. aureus isolates from healthy individuals.

Mupirocin resistance in patients colonized with methicillin-resistant Staphylococcus aureus in a surgical intensive care unit.

Nasal colonization with methicillin-resistant Staphylococcus aureus (MRSA) can be a precursor to serious infection, and decolonization with topical mupirocin has been studied as a means of preventing clinical infection. Mupirocin resistance in patients with MRSA has been reported, usually in the context of widespread mupirocin use. Patients admitted to a surgical intensive care unit (SICU) had nasal swab cultures for MRSA performed at admission, weekly, and at discharge in an active surveillance program. Collected MRSA isolates were tested for mupirocin resistance, and molecular analysis was performed. Clinical data on the characteristics and outcomes of the patients who stayed in the SICU for >48 h were collected prospectively. Of the 302 MRSA isolates available for testing, 13.2% were resistant to mupirocin, with 8.6% having high-level resistance (minimum inhibitory concentration, >or=512 microg/mL) and 4.6% having low-level resistance (minimum inhibitory concentration, 8-256 microg/mL). Patients admitted to the SICU for >48 h who were colonized with mupirocin-resistant MRSA were more likely to have been admitted to our hospital during the previous year (P=.016), were older (P=.009), and had higher in-hospital mortality (16% vs. 33%; P=.027), compared with patients colonized with mupirocin-susceptible MRSA. Molecular analysis of the mupirocin-resistant isolates revealed that 72.5% of isolates contained staphylococcal cassette chromosome mec II. Repetitive sequence polymerase chain reaction typing revealed that high-level mupirocin resistance was present in multiple clonal groups. The rate of mupirocin use hospital-wide during the study period was 6.08 treatment-days per 1000 patient-days. We documented a high rate of mupirocin resistance in MRSA isolates from SICU patients, despite low levels of in-hospital mupirocin use.

Portación nasal de Streptococcus pneumoniae en adulto mayor y su respuesta frente a la vacunación antineumocócica

S pneumoniae is the main cause of community-acquired pneumonia in the elderly, group that concentrates 95% of deaths. To assess the prevalence of nasal carriage of S pneumoniae in institutionalized elderly patients. One hundred eighteen institutionalized subjects aged over 60 years (65 males) were enrolled. Since they were also participating in a controlled protocol related to the immunogenicity of an anti-pneumococcal vaccine, our investigation was also blind and randomized. According to randomization, they received pneumococcal or tetanic vaccine. Nasal swab cultures were taken at the beginning of the trial and two months after vaccination. According to recommended methods, we identified S pneumoniae, the serotypes and their antimicrobial susceptibility. In the first nasal sample, 16% of subjects were positive for S pneumoniae. The second sample was positive in 12%. Of the 33 isolated serotypes, 9.1% demonstrated intermediate resistance to penicillin and 3.3% were resistant to chloramphenicol. The study demonstrated a greater percentage of colonized patients than in the general population. The isolated serotypes are the same that cause invasive diseases in this age group, according to data of the Institute of Public Health of Chile. There were no differences in the percentage of colonization between subjects vaccinated against S pneumoniae and control groups, after two months of follow up. Isolated strains had a low resistance to penicillin. High level resistance was not observed.

Lymphocutaneous and nasal sporotrichosis in a dog from Southern Italy: Case Report

Sporotrichosis is a chronic, granulomatous and usually lymphocutaneous infection of humans and animals caused by the dimorphic fungus, Sporothrix schenckii. This study reports a case of lymphocutaneous and nasal sporotrichosis in a hunting dog with a three month history of non-healing skin lesions. Cytological examination of nasal discharge and of the material collected from ulcerated skin surfaces showed a few cigar-shaped organisms within macrophages. Fungal cultures of nasal and ulcerated skin swabs yielded colonies of S. schenckii. The dog received oral itraconazole but died of unrelated causes. Necropsic examination was not performed.

Staphylococcus aureusNasal Carriage Is Associated with Glucocorticoid Receptor Gene Polymorphisms

The aim of this study was to determine whether polymorphisms of the glucocorticoid receptor gene, influencing glucocorticoid sensitivity, are associated with persistent nasal carriage of Staphylococcus aureus. Two nasal swab cultures were obtained from each of 2,929 participants. Subjects were classified as persistent carriers (n=563) if both cultures were positive. GG homozygotes of the exon 9beta polymorphism were associated with a 68% reduced risk of persistent S. aureus nasal carriage, whereas carriers of the codon 23 lysine allele displayed an 80% increased risk. Thus, genotype-dependent variation in the sensitivity to glucocorticoids is associated with tolerance toward staphylococcal nasal colonization.

Efficacy of rifampicin in eradication of carrier state of Staphylococcus aureus in anterior nares with recurrent furunculosis.

To compare the frequency of detection of Staphylococcus aureus carrier state in anterior nares of the patients suffering from recurrent furunculosis with the normal population and to determine the efficacy of rifampicin in eradication of the carrier state. Quasi-experimental study. Skin Department of Combined Military Hospital, Peshawar and Multan, from March 2004 to December 2005. The study consisted of 80 individuals. They were placed in two groups. Group I comprised of 40 patients suffering from recurrent furuncles and group II included 40 healthy adults, kept as controls. Nasal swab was taken from the individuals belonging to both the groups, when they first reported to skin OPD. The patients who were suffering from furuncles were treated with co-amoxiclav 375 or 625 mg three times a day. The patients in whom S. aureus carrier state was detected were again divided into two groups. Group 1 was prescribed rifampicin 450-600 mg daily (depending on the body weight) for 10 days, while the group 2 was not offered any treatment. After this course, a second nasal swab was taken and submitted for cultures. Among the 40 patients belonging to group I, S. aureus carrier state was detected in 23 (57.5%), while in group II the carrier state was found in 8 (20%) individuals (p<0.001). Among the 13 patients who received rifampicin, 10 got cured of carrier state, while in 3 patients nasal swab was still positive after a course of rifampicin. In 10 patients, who were not offered any treatment, the nasal swabs remained positive (p<0.001). These patients were followed-up in skin OPD for another 3 months, and did not develop any recurrence of the infection. Nasal swab for detection of S. aureus carrier state should be done in all patients of recurrent furunculosis. If the nasal swab culture is positive, then as the infection gets cured, the patients should receive a course of rifampicin for 10 days. This may eradicate the carrier state in majority of cases and prevent the recurrence of the infection.

Risk factors for ICU-acquired methicillin-resistant Staphylococcus aureus infections

Methicillin-resistant Staphylococcus aureus (MRSA) is a major nosocomial pathogen that causes severe morbidity and mortality in many hospitals worldwide, and MRSA infections are frequent in intensive care units (ICUs). A prospective study was implemented to investigate the risk factors for ICU-acquired MRSA infections. This study was conducted in surgical and neurologic ICUs from May to November 2003. The patients staying in ICUs more than 48 hours were included in the study. All of the patients were visited daily, and data were recorded on individual forms for each patient until discharge or death. Nasal swab cultures were done within 48 hours of ICU admission and repeated every week until the patients colonized with MRSA or were discharged from ICUs. ICU-acquired MRSA infection was diagnosed when MRSA was isolated from the infected site. Overall, 249 patients were followed during the study. MRSA infection was detected in 21 (8.4%) of these patients. The most frequent infection was primary bloodstream infection (10/21, 47%). It was followed by pneumonia (8/21, 38%) and surgical site infection (3/21, 14%). Nasal MRSA colonization was detected in 59 (23.7%) patients, and 12 of them (20.3%) developed MRSA infection. In univariate analysis, hospitalization period in an ICU, intraabdominal and orthopedic pathologies, mechanical ventilation, central venous catheter insertion, total parenteral nutrition, previous antibiotic use, surgical ICU stay, nasal MRSA colonization, and presence of more than 2 patients having nasal colonization in the same ICU at the same time were found significant for MRSA infections. In multivariate analysis; hospitalization period in an ICU (OR, 1.090; 95% CI: 1.038-1.144, P = .001), central venous catheter insertion (OR, 1.822; 95% CI: 1.095-3.033, P = .021), previous antibiotic use (OR, 2.337; 95% CI: 1.326-4.119, P = .003) and presence of more than 2 patients having nasal colonization in the same ICU at the same time (OR, 1.398; 95% CI: 1.020-1.917, P = .037) were independently associated with MRSA infections. According to the our results, hospitalization period in an ICU, presence of patients colonized with MRSA in the same ICU at the same time, previous antibiotic use, and central venous catheter insertion are independent risk factors for ICU-acquired MRSA infections. Detection of these factors helps to decrease the rate of MRSA infections in the ICUs.

Streptococcus pneumoniae and Noncapsular Haemophilus influenzae Nasal Carriage and Hand Contamination in Children

Australian Indigenous children living in remote areas have rates of tympanic membrane perforation as high as 60%, almost 100 times the prevalence in urban child care settings (<1%). Relative rates of pneumococcal nasal carriage do not reflect this difference in disease risk. Cross-sectional comparison of nasal carriage and hand contamination in children younger than 4 years of age from urban child-care centers and Indigenous children 3-7 years of age from a remote community. Almost identical methods of nasal swab collection, transport and culture were used. Data on pneumococcal antimicrobial susceptibility patterns and serotypes are also reported. For Indigenous children compared with children in child care, the relative risk of nasal carriage of either pneumococcus or noncapsular Haemophilus influenzae was <2-fold [relative risk, 1.7; 95% confidence interval (CI), 1.5, 1.9], the risk of simultaneous nasal carriage was almost 3-fold (78% versus 28%; relative risk, 2.9; 95% CI 2.3, 3.5), and the risk of pneumococcal hand contamination was 8-fold higher (37% versus 4%; relative risk, 8.4; 95% CI 4.6, 15.2). For simultaneous hand contamination, the risk was 23-fold (8% versus 0.3%; relative risk, 23.1; 95% CI 2.9, 185.4). Remote Indigenous children also had a more diverse serotype distribution (25 versus 14 serotypes identified). Simultaneous nasal carriage of Streptococcus pneumoniae and H. influenzae and hand contamination are simple indicators of risk for use in studies of otitis media in populations at risk for tympanic membrane perforation.

Are Active Microbiological Surveillance and Subsequent Isolation Needed to Prevent the Spread of Methicillin-Resistant Staphylococcus aureus?

Infection-control strategies usually combine several interventions. The relative value of individual interventions, however, is rarely determined. We assessed the effect of daily microbiological surveillance alone (e.g., without report of culture results or isolating colonized patients) as an infection-control measure on the spread of methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) in a medical intensive care unit (MICU). Colonization of patients with MSSA and MRSA was assessed by cultures of nasal swabs obtained daily and, if a patient was intubated, by cultures of additional endotracheal aspirates. Pulsed-field gel electrophoresis was used to determine relatedness between MSSA or MRSA isolates in surveillance cultures (i.e., cultures of nasal swab specimens obtained daily) and those in clinical cultures (i.e., any other culture performed for clinical purposes). Adherence to infection-control measures by health care workers (HCWs) was determined by observations of HCW-patient interaction. During a 10-week period, surveillance cultures were performed for 158 patients. Fifty-five patients (34.8%) were colonized with MSSA, and 9 (5.7%) were colonized with MRSA. Sixty-two patients were colonized before admission to the hospital (53 had MSSA, and 9 had MRSA). Two patients appeared to have acquired MSSA in the MICU, but, on the basis of genotyping analysis, we determined that this was not the result of cross-acquisition. Surveillance cultures and genotyping of MRSA and MSSA isolates demonstrated the absence of cross-transmission among patients in the MICU, despite ongoing introduction of these pathogens. Reporting culture results and isolating colonized patients, as suggested by some guidelines, would have falsely suggested the success of such infection-control policies.

Impact de la colonisation nasale par le Staphylococcus aureus résistant à la méticilline dans une unité de soins de suite gériatrique

To evaluate the impact of nasal carriage of Methicillin Resistant Staphylococcus aureus (MRSA) on antibiotic cost, infection morbidity, mortality and length of stay in a geriatric population. 341 consecutive elderly patients (mean age 83.4 +/- 8.7 years) admitted to an intermediate care facility were prospectively include between November 1998 and October 1999. Nasal swab cultures were taken on admission. In sixty patients (17.6%) no nasal swab was taken. Among the 281 patients screened, 52 were identified as MRSA carriers. The principle predictive factors were: diabetes (p=0,046), sores (p=0,03), malnutrition (p=0,02), polypathology (p=0,02) and prolongation of previous hospitalisation (p=0,09). Nasal carriage of MRSA on admission to the facility was not a deleterious prognostic factor regarding duration of stay, infectious morbidity and antibiotic cost, but was associated with higher mortality risk.

Predicting the Staphylococcus aureus nasal carrier state: derivation and validation of a "culture rule".

To study determinants and risks of Staphylococcus aureus nasal carriage, adequate differentiation between the different S. aureus carrier states is obligatory. We set out to develop a "culture rule" capable of differentiating between persistent and intermittent or noncarriers that uses a minimum of nasal swab cultures. In 51 healthy volunteers (derivation cohort), 12 quantitative nasal cultures were performed to establish S. aureus nasal carriage states. Persons with 11 or 12 cultures positive for S. aureus were classified as persistent carriers, and those with negative results of all cultures were classified as noncarriers. All other persons were classified as intermittent carriers. By means of logistic regression and receiver operating characteristic (ROC) curves, a culture rule was derived. This culture rule was subsequently validated in 106 participants of an ongoing study in 3882 elderly persons, again with the use of 12 quantitative nasal cultures. In both cohorts, the positive predictive value of 2 consecutive positive culture results for persistent carriage was 79%. The model best differentiating between persistent and intermittent or noncarriers used the number of positive culture results combined with the amount of S. aureus in these cultures. By using the outcome of 2 cultures, the areas under the ROC curves were 0.981 (95% confidence interval [CI], 0.949-1.0) for the derivation cohort and 0.936 (95% CI, 0.881-0.990) for the validation cohort. Combining qualitative and quantitative results of 2 nasal swab cultures accurately predicted the persistent S. aureus carriage state with a reliability of 93.6%. Thus, this culture rule can be used in studies of determinants and risks of S. aureus nasal carriage.

Risk Factors for Staphylococcus aureus Colonization in a Cardiac Surgery Population

BACKGROUND/OBJECTIVES: The objective of this project was to identify the prevalence of methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA) carriage among cardiac surgery patients and to identify associated risk factors for MSSA and MRSA colonization. METHODS: Nasal swab cultures for MSSA and MRSA were obtained on 173/238 (73%) patients admitted to Barnes-Jewish hospital (BJH) for cardiac surgery from September through December 2002. Patients were swabbed the day of surgery in the pre-operative holding area. Variables were collected by retrospective chart review to determine medical and healthcare exposure risk factors associated with MSSA /MRSA colonization for 34 cases compared to all 139 culture-negative patients identified during the swabbing period. Univariate analysis was performed using Chi-square and Fisher's Exact to test for statistical significance. RESULTS: Of patients tested 34/173 (20%) were colonized with S. aureus; 27/173 (16%) were colonized with MSSA; 7/173 (4%) were colonized with MRSA. Analysis identified no risk factors that were associated with S. aureus colonization. Congestive heart failure (p= 0.27), chronic obstructive pulmonary disease (p= 0.13), renal failure (p=0.42), diabetes (p=0.55), and hospitalization in the past 12 months (p= 0.39) were similar in patients with and without MRSA. Steroid use within 30 days of admission (p= 0.02), presence of an invasive device (central line, dialysis catheter, defibrillator, prosthetic joint) (p= 0.01), and long-term/group home residence (p= 0.001) were significantly associated with MRSA colonization. CONCLUSIONS: The percent of BJH cardiac surgery patients colonized with MSSA and MRSA was lower than reported in the literature. Risk factors associated with MRSA colonization were similar to the literature. Identification of risk factors for colonization with MSSA/MRSA in specific patient populations could be useful to enhance surgical antibiotic prophylaxis.