Histological score for degrees of severity in an implant-associated infection model in mice.

INTRODUCTION: Several scores were introduced to diagnose and to classify osteomyelitis in practice. Mouse models are often used to study the pathophysiology of bone infection and to test therapeutic strategies. Aim of the present study was to design a score to diagnose and quantify implant-associated infection in a murine experimental model. MATERIALS AND METHODS: Four independent parameters were developed: existence of callus, consolidation of the fracture, structural changes of the medullary cavity and number of bacteria. The score was assessed in a standardized implant-associated mouse model with 35 BALB/c-mice. The left femur was osteotomized, fixed by a titanium locking plate and infection was induced by inoculation of Staphylococcus aureus into the fracture gap. For the sham group, the procedure was performed without inoculation of bacteria. The score was assessed on days 7, 14 and 28. Each item of the score showed lower values for the infection group compared to the controls after 4 weeks. RESULTS: Regardless of the assessed time point, the overall total score was significantly higher in the control group compared to the infection group (p < 0.0001). Analysis revealed a sensitivity of 0.85, specificity of 1.0, negative predictive value of 0.67 and positive predictive value of 1.0. CONCLUSION: The proposed score assessing severity of fracture-related infection in an implant-associated murine model was easy to access, feasible to diagnose and estimate bone healing and infection in a murine bone infection with a high sensitivity. Therefore, this score might be a useful tool to quantify infection-related changes after fracture in further future preclinical studies.

What is behind phylogenetic analysis of hospital-, community- and livestock-associated methicillin-resistant Staphylococcus aureus?

Methicillin-resistant Staphylococcus aureus (MRSA) has been shown to be the predominant life-threatening pathogen in Egypt. MRSA is a major cause of severe healthcare-associated (HA) infections. During the last decades, the incidence of community-associated (CA) MRSA infections has a complex epidemiology arising from the circulation of different strains in the general population. Moreover, livestock-associated (LA) MRSA emerged recently becomes an emerging threat to public health. Therefore, it is important to illuminate the differences between CA-, HA- and LA-MRSA to shed light on their genetic diversity and evolution. This study presents the first data on analysing the correlation between CA-, LA- and HA-MRSA using antibiogram typing, molecular characteristics and antimicrobial resistance and virulence genes' profiles. Overall, HA-MRSA strains tended to be multidrug resistant and less virulent than both LA- and CA-MRSA strains. Importantly, CA-MRSA strains had a high homology with each of HA- and LA-MRSA. However, no similarity was observed between HA- and LA-MRSA. Our findings suggest that the epidemiological changes in genetic behaviour between HA- and LA-MRSA are due to the presence of CA-MRSA confirming that CA-MRSA has created a public health crisis worldwide.

Species and antimicrobial susceptibility testing of coagulase-negative staphylococci in periprosthetic joint infections.

The objective was to evaluate the distribution of coagulase-negative staphylococci (CNS) involved in periprosthetic-joint infections (PJIs) and to describe their susceptibility profile to antibiotics. We conducted a multicentre retrospective study in France, including 215 CNS PJIs between 2011 and 2015. CNS PJIs involved knees in 54% of the cases, hips in 39%, other sites in 7%. The distribution of the 215 strains was: Staphylococcus epidermidis 129 (60%), Staphylococcus capitis 24 (11%), Staphylococcus lugdunensis 21 (10%), Staphylococcus warneri 8 (4%), Staphylococcus hominis 7 (3%), Staphylococcus haemolyticus 7 (3%). More than half of the strains (52.1%) were resistant to methicillin, 40.9% to ofloxacin, 20% to rifampicin. The species most resistant to antibiotics were S. hominis, S. haemolyticus, S. epidermidis, with 69.7% of the strains resistant to methicillin and 30% simultaneously resistant to clindamycin, cotrimoxazole, ofloxacin and rifampicin. No strain was resistant to linezolid or daptomycin. In this study on CNS involved in PJIs, resistance to methicillin is greater than 50%. S. epidermidis is the most frequent and resistant species to antibiotics. Emerging species such S. lugdunensis, S. capitis and Staphylococcus caprae exhibit profiles more sensitive to antibiotics. The antibiotics most often active in vitro are linezolid and daptomycin.

Diagnosing intramammary infection: Controlling misclassification bias in longitudinal udder health studies.

Using imperfect tests may lead to biased estimates of disease frequency and of associations between risk factors and disease. For instance in longitudinal udder health studies, both quarters at risk and incident intramammary infections (IMI) can be wrongly identified, resulting in selection and misclassification bias, respectively. Diagnostic accuracy can possibly be improved by using duplicate or triplicate samples for identifying quarters at risk and, subsequently, incident IMI. The objectives of this study were to evaluate the relative impact of selection and misclassification biases resulting from IMI misclassification on measures of disease frequency (incidence) and of association with hypothetical exposures. The effect of improving the sampling strategy by collecting duplicate or triplicate samples at first or second sampling was also assessed. Data sets from a hypothetical cohort study were simulated and analyzed based on a separate scenario for two common mastitis pathogens representing two distinct prevailing patterns. Staphylococcus aureus, a relatively uncommon pathogen with a low incidence, is identified with excellent sensitivity and almost perfect specificity. Coagulase negative staphylococci (CNS) are more prevalent, with a high incidence, and with milk bacteriological culture having fair Se but excellent Sp. The generated data sets for each scenario were emulating a longitudinal cohort study with two milk samples collected one month apart from each quarter of a random sample of 30 cows/herd, from 100 herds, with a herd-level exposure having a known strength of association. Incidence of IMI and measure of association with exposure (odds ratio; OR) were estimated using Markov Chain Monte Carlo (MCMC) for each data set and using different sampling strategies (single, duplicate, triplicate samples with series or parallel interpretation) for identifying quarters at risk and incident IMI. For S. aureus biases were small with an observed incidence of 0.29 versus a true incidence of 0.25IMI/100 quarter-month. In the CNS scenario, diagnostic errors in the two samples led to important selection (40IMI/100 quarter-month) and misclassification (23IMI/100 quarter-month) biases for estimation of IMI incidence, respectively. These biases were in opposite direction and therefore the incidence measure obtained using single sampling on both the first and second test (29IMI/100 quarter-month) was exactly the true value. In the S. aureus scenario the OR for association with exposure showed little bias (observed OR of 3.1 versus true OR of 3.2). The CNS scenario revealed the presence of a large misclassification bias moving the association towards the null value (OR of 1.7 versus true OR of 2.6). Little improvement could be brought using different sampling strategies aiming at improving Se and/or Sp on first and/or second sampling or using a two out of three interpretation for IMI definition. Increasing number of samples or tests can prevent bias in some situations but efforts can be spared by holding to a single sampling approach in others. When designing longitudinal studies, evaluating potential biases and best sampling strategy is as critical as the choice of test.

[Acute haematogenous osteomyelitis in children : Diagnostic algorithm and treatment strategies]. / Akute hämatogene Osteomyelitis im Wachstumsalter : Diagnostischer Algorithmus und Behandlungsstrategien.

Acute haematogenous osteomyelitis (AHO) in children is a severe condition. A delay in diagnosis and insufficient treatment may result in deformities, chronicity and sepsis. Therefore a structured diagnostic workup has to be followed in order to diagnose or rule out osteomyelitis. To identify the causative agent for targeted antibiotic treatment, a bone biopsy or puncture should be performed. However, approximately 25% of cases are culture-negative even after biopsy. The knowledge of the typical age-dependent bacterial spectrum is essential for empirical antibiotic therapy. The principal causative organism is Staphylococcus aureus. Surgery is not routinely required in paediatric acute osteomyelitis but surgical intervention is indicated if an abscess is detected. Secondary septic arthritis is a serious complication which has to be treated immediately by surgical intervention. Nevertheless, complete regeneration can be expected in up to 80% of children with AHO.

Malignant Otitis Externa: A Novel Stratification Protocol for Predicting Treatment Outcomes.

OBJECTIVES: 1) Stratify malignant otitis externa into severe and nonsevere disease categories. 2) Predict treatment courses and outcomes based on this stratification. SETTING: Tertiary center. PATIENTS: Retrospective review 2004 to 2014; 28 patients. Inclusion criteria are a diagnosis by senior authors, radiographic evidence of disease, admission for intravenous antibiotics/debridement, minimum 1 year of follow-up. INTERVENTIONS: Severe group stratification if two or more of the following: cranial nerve VII palsy, fungal positive culture, relapse, surgery performed, major radiographic findings. All other patients stratified to nonsevere group. MAIN OUTCOME MEASURES: Cure, alive/refractory disease, death by disease, death by other cause. Secondary measures are antibiotic duration and number of disease-related admissions. RESULTS: Forty-three percent (12 of 28) and 57% (16 of 28) of patients stratified into the severe and nonsevere groups. The severe group had significantly more adverse disease-specific outcomes than the nonsevere group (7 of 12 versus 0 of 16; p = 0.002). Disease-specific mortality was 42% and 0% in the severe and nonsevere groups, respectively. The severe group had longer antibiotic courses (12.8 versus 6.9 wk; p = 0.01) and more disease-related admissions/relapses (1.6 versus 1, p < 0.001). Only four of 12 severe group patients achieved cure. All but two nonsevere patients achieved cure, with those two dying of other causes. CONCLUSION: A subgroup of malignant otitis externa may exist that is not as susceptible to parenteral antibiotics and local debridement. A combination of clinical and radiographic findings may be useful for stratifying patients into severe/nonsevere categories. Patients with severe disease may be more likely to die of their disease and have worse treatment courses such that additional surgical intervention may be indicated.

Diagnosis and classification of granulomatosis with polyangiitis (aka Wegener's granulomatosis).

Granulomatosis with polyangiitis (GPA, formerly known as Wegener's Granulomatosis) is an autoimmune small vessel vasculitis which is highly associated with anti-neutrophil cytoplasmic antibodies (ANCA). The hallmarks of this condition are systemic necrotising vasculitis, necrotising granulomatous inflammation, and necrotising glomerulonephritis. The aetiology of granulomatosis with polyangiitis is linked to environmental and infectious triggers inciting onset of disease in genetically predisposed individuals. Anti-neutrophil cytoplasmic antibodies are pathogenic and play an important role in the pathogenesis of this disease, although ANCA positivity is not essential for a clinical diagnosis of granulomatosis with polyangiitis. Granulomatosis with polyangiitis is diagnosed based on clinical manifestations of systemic vasculitis and histological evidence of necrotising vasculitis or granulomatous inflammation. This small vessel vasculitis may present as limited disease of the ears, nose and upper airways or mild, moderate or severe systemic disease. Immunosuppression and adjuvant therapies have contributed to the improved prognosis of granulomatosis with polyangiitis over the past decades. Treatment strategies are tailored to the severity of the disease. They are based on published evidence of the efficacy and safety of the immunosuppressive drugs indicated to manage active vasculitis and maintain clinical remission. This review will summarise the history, aetiology, pathogenesis, classification, diagnosis and management of granulomatosis with polyangiitis.

Estimated burden of methicillin-resistant Staphylococcus aureus in California hospitals after changes to administrative codes, 2005-2010.

We assess the impact of revised International Classification of Diseases, Ninth Revision, codes on methicillin-resistant Staphylococcus aureus burden in California hospitals. Codes were rapidly adopted, demonstrating new capture of colonization and continued relatively stable capture of infections. Nevertheless, despite new colonization codes, coded data demonstrated poor retention between serial hospitalizations.

High Resolution Typing by Whole Genome Mapping Enables Discrimination of LA-MRSA (CC398) Strains and Identification of Transmission Events.

After its emergence in 2003, a livestock-associated (LA-)MRSA clade (CC398) has caused an impressive increase in the number of isolates submitted for the Dutch national MRSA surveillance and now comprises 40% of all isolates. The currently used molecular typing techniques have limited discriminatory power for this MRSA clade, which hampers studies on the origin and transmission routes. Recently, a new molecular analysis technique named whole genome mapping was introduced. This method creates high-resolution, ordered whole genome restriction maps that may have potential for strain typing. In this study, we assessed and validated the capability of whole genome mapping to differentiate LA-MRSA isolates. Multiple validation experiments showed that whole genome mapping produced highly reproducible results. Assessment of the technique on two well-documented MRSA outbreaks showed that whole genome mapping was able to confirm one outbreak, but revealed major differences between the maps of a second, indicating that not all isolates belonged to this outbreak. Whole genome mapping of LA-MRSA isolates that were epidemiologically unlinked provided a much higher discriminatory power than spa-typing or MLVA. In contrast, maps created from LA-MRSA isolates obtained during a proven LA-MRSA outbreak were nearly indistinguishable showing that transmission of LA-MRSA can be detected by whole genome mapping. Finally, whole genome maps of LA-MRSA isolates originating from two unrelated veterinarians and their household members showed that veterinarians may carry and transmit different LA-MRSA strains at the same time. No such conclusions could be drawn based spa-typing and MLVA. Although PFGE seems to be suitable for molecular typing of LA-MRSA, WGM provides a much higher discriminatory power. Furthermore, whole genome mapping can provide a comparison with other maps within 2 days after the bacterial culture is received, making it suitable to investigate transmission events and outbreaks caused by LA-MRSA.

Can implantable cardiac electronic device infections be defined as 'early' or 'late' based on the cause of infection?

Implantable cardiac electronic device (ICED) infections are a major cause of morbidity and mortality. Understanding the pathogenesis of these infections is important in their prevention and management. We hypothesized that ICED infections could be classified as 'early' or 'late', based on differences in microbiological cause within or beyond 1 year of implantation, respectively. A comprehensive review of the literature was undertaken to test this hypothesis. Prosthetic valve endocarditis cases were included for comparison. Articles were included if the time from device implantation to infection, definite evidence of infection (pocket/bacteraemia/endocarditis) and a positive microbiological diagnosis were included. There were no statistically significant differences in microbiology to support a 1 year cut-off between early and late ICED infection. Staphylococcus aureus and coagulase-negative staphylococci were the predominant causes of ICED infection both within and beyond 1 year of ICED implantation. To further assess the microbiological causes of ICEDs and their implications for pathogenesis a large-scale multi-centre study is required.

Emergence of methicillin-resistant Staphylococcus aureus in the Maternity Hospital, Kuwait.

OBJECTIVE: To establish the relatedness of methicillin-resistant Staphylococcus aureus (MRSA) isolates in the Maternity Hospital, Kuwait. MATERIALS AND METHODS: A total of 22 MRSA were isolated from 20 neonates and 1 mother in the Special Care Unit, Maternity Hospital, Kuwait. They were characterized using antibiogram, pulsed-field gel electrophoresis (PFGE), SCCmec typing, spa typing and multi locus sequence typing (MLST), and were screened for genes encoding Panton Valentine leukocidin (PVL) and capsular polysaccharide types 5 and 8. RESULTS: The isolates were resistant to cadmium acetate (n = 22 or 100%), trimethoprim (n = 13 or 59.1%), gentamicin (n = 7 or 31.8%), ciprofloxacin (n = 5 or 22.7%), erythromycin and clindamycin (n = 2 or 9.1%), tetracycline (n = 2 or 9.1%) and fusidic acid (n = 2 or 9.1%). Eight isolates contained genes for PVL while 15 and 6 carried genes for types 5 and 8 capsular polysaccharide, respectively. Molecular typing distinguished 12 clones. Ten of these clones consisted of 20 isolates belonging to ST60-SCCmec-IV-t3935 (5 isolates), ST6-SCCmec-IV-t6269 (4 isolates), ST194-SCCmec-IV-t6892 (3 isolates), ST1-SCCmec-V-t2962 (2 isolates) and 1 isolate each of ST77-SCCmec-IV-t339, ST935-SCCmec-V-t1084, ST1317-SCCmec-V-t1548, ST9-SCCmec-V-t5801, ST627-SCCmec-IV-t1340 and ST2148-SCCmec-IV-t2810. CONCLUSION: The study demonstrated the emergence of MRSA including novel ST60 and ST194 clones at the Maternity Hospital in Kuwait.

Rise of CC398 lineage of Staphylococcus aureus among Infective endocarditis isolates revealed by two consecutive population-based studies in France.

Staphylococcus aureus isolates from two prospective studies on infective endocarditis (IE) conducted in 1999 and 2008 and isolated from non-IE bacteremia collected in 2006 were spa-typed and their virulence factors were analyzed with a microarray. Both populations were genetically diverse, with no virulence factors or genotypes significantly more associated with the IE isolates compared with the non-IE isolates. The population structure of the IE isolates did not change much between 1999 and 2008, with the exception of the appearance of CC398 methicillin-susceptible Staphylococcus aureus (MSSA) isolates responsible for 5.6% of all cases in 2008. In 1999, this lineage was responsible for no cases. The increasing prevalence of S. aureus in IE is apparently not the result of a major change in staphylococcal population structure over time, with the exception of the emerging CC398 MSSA lineage.

Molecular characterization of Staphylococcus aureus isolated from children with adenoid hypertrophy: emergence of new spa types t7685 and t7692.

OBJECTIVE: Adenoids have been associated with the pathogenesis of acute, recurrent and chronic infectious diseases of the upper respiratory system and their hypertrophy is one of the most common causes of upper airway obstruction affecting children. In this study, the characteristics of Staphylococcus aureus isolates from patients who had undergone adenoidectomy were investigated via spa typing method. METHODS: A total of 113 children with adenoid hypertrophy who underwent adenoidectomy during September 2009 to November 2010, were included in the study. The isolates were identified to the species level as S. aureus using standard biochemical methods, following which the amplification and sequencing of the spa gene X region were carried out. RESULTS: S. aureus was found in the adenoid tissue of 26 (23%) patients. Out of the 26 S. aureus isolates, 5 (19%), 3 (11.5%) and 3 (11.5%) were resistant to tetracycline, erythromycin and oxacillin respectively. All the isolates were susceptible to vancomycin, rifampin, ciprofloxacin, gentamicin, mupirocin and quinupristin-dalfopristin and were typed using spa typing method. All the isolates were found to include 21 spa types, including two previously unreported types (t7685 and t7692). The most prevalent spa types were t7685 (11.5%), t230 (8%), t325 (8%) and t1149 (8%). CONCLUSION: This study demonstrates that the prevalence rate of S. aureus in the adenoid tissue of the children assessed was 23%. An interesting point to note was the dominance of the spa type t7685 that has not been previously reported by other studies.

Molecular characterization of methicillin-resistant Staphylococcus aureus isolates in Algeria.

INTRODUCTION: The epidemiology of Staphylococcus aureus has changed radically since 1999, in particular, methicillin-resistant S. aureus (MRSA), originally restricted to hospital, has emerged as a significant pathogen in the community, and true community-acquired MRSA (CA-MRSA) infections have been reported in patients with no clear risk factors. CA-MRSA strains frequently produce Panton-Valentine leukocidin (PVL). OBJECTIVES: The objectives of this study were: (i) to monitor the prevalence of PVL and toxic shock syndrome toxin-1 (TSST-1) isolates MRSA; (ii) to identify the staphylococcal cassette chromosome (SCCmec) types of MRSA isolates. MATERIAL AND METHODS: Sixty-four isolates, collected between 2005 and 2007 in Didouche Mourad hospital of Algeria. The isolates were identified by conventional methods. The antibiotic susceptibility of the isolates was performed using the disk diffusion method and automat Vitek2. The presence of gene mecA, the genes encoding SCCmec type, PVL and TSST-1 toxins were investigated by real-time PCR. RESULTS: All strains were gene mecA positives, 32 (50%) harboured SCCmec IV type, 28 (43.75%) harboured SCCmec V type. 19 (29.68%) have been identified positive for the leukocidin toxin (PVL), they harboured SCCmec type IV. The virulence factor TSST-1 was not present among these isolates. CONCLUSION: These results show a high prevalence of PVL-positive H-MRSA in our wards.

Public health surveillance for methicillin-resistant Staphylococcus aureus: comparison of methods for classifying health care- and community-associated infections.

OBJECTIVES: We compared 3 methods for classifying methicillin-resistant Staphylococcus aureus (MRSA) infections as health care associated or community associated for use in public health surveillance. METHODS: We analyzed data on MRSA infections reported to the Michigan Department of Community Health from October 1, 2004, to December 31, 2005. Patient demographics, risk factors, infection information, and susceptibility were collected for 2151 cases. We classified each case by the health care risk factor, infection-type, and susceptibility pattern methods and compared the results of the 3 methods. RESULTS: Demographic, clinical, and microbiological variables yielded similar health care-associated and community-associated distributions when classified by risk factor and infection type. When 2 methods yielded the same classifications, the overall distribution was similar to classification by 3 methods. No specific combination of 2 methods was superior. CONCLUSIONS: MRSA categorization by 2 methods is more accurate than it is by a single method. The health care risk factor and infection-type methods yield comparable classification results. Accuracy is increased by using more variables; however, further research is needed to identify the optimal combination.

Characterization of community and hospital Staphylococcus aureus isolates in Southampton, UK.

Staphylococcus aureus infections are a burden to healthcare systems. There remains a lack of understanding on the relative contributions of S. aureus infection in the healthcare and community settings. In this study, 59 S. aureus isolates were selected for molecular analysis. The mobile variant staphylococcal cassette chromosome mec type IV was present in both healthcare-associated meticillin-resistant S. aureus (HA-MRSA) and community-associated MRSA (CA-MRSA), as was the Panton-Valentine leukocidin gene. PFGE identified 24 distinct clonal groups whilst multi-locus sequence typing identified 26 different sequence types, including four with new combinations of alleles. This is the first time, to our knowledge, that a selection of CA and HA MSSA and MRSA strains have been subjected to molecular analysis and comparison in the UK. Definitions for CA-MRSA need further debate as the movement of strains between healthcare and community settings is confounding the use of epidemiological definitions.

Health care-associated and community-associated methicillin-resistant Staphylococcus aureus infections: A comparison of definitions.

BACKGROUND: Different approaches are used to classify methicillin-resistant Staphylococcus aureus (MRSA) infections as either community-acquired (CA-MRSA) or health care-associated MRSA (HA-MRSA). METHODS: We collected information on patients seen at the Atlanta Veterans Affairs Medical Center with MRSA infections from June 2007 through May 2008. We classified MRSA infections as either HA or CA using an epidemiologic definition and an antibiotic susceptibility phenotype rule. We used multivariate logistic regression to describe factors significantly associated with HA-MRSA infections compared with CA-MRSA infections. RESULTS: Using the epidemiologic definition to classify infections, we found white race (odds ratio [OR], 3.2; 95% confidence interval [CI]: 2.0-5.2), oral antibiotics in the 3 months prior (OR, 4.0; 95% CI: 1.5-10.4), and endoscopy in the past year (OR, 3.8; 95% CI: 1.8-8.0) were significantly associated with health care-associated infections. When classifying by the resistance phenotype rule, we found hospitalization in the past year (OR: 1.8; 95% CI: 1.1-3.1) and an indwelling device in the past year (OR: 6.3; 95% CI: 2.5-15.8) were significantly associated with health care-associated infections. CONCLUSION: We found few differences between CA- and HA-MRSA infections, regardless of how health care-association was defined. We believe that the migration of CA-MRSA into health care settings and the recent increasing antibiotic resistance of CA-MRSA strains contribute to the lack of factors associated with HA (vs CA) MRSA.

Methicillin-resistant Staphylococcus aureus (MRSA) ST398 associated with clinical and subclinical mastitis in Belgian cows.

Methicillin-resistant Staphylococcus aureus (MRSA) is infrequently reported in mastitis. Yet, as in many other countries, the prevalence of methicillin resistance among S. aureus from mastitis is currently unknown in Belgium. To elucidate this, the presence of mecA was investigated in 118 S. aureus strains originating from diagnostic mastitis milk samples from 118 different farms experiencing S. aureus mastitis. MRSA strains were characterized by disk diffusion susceptibility testing, spa-typing, MLST and SCCmec-typing. In an additional study, four MRSA-positive farms were selected to assess the in-herd prevalence of MRSA, by sampling all cows in lactation. Isolated MRSA strains were similarly characterized. The mecA gene was detected in 11 (9.3%) of the 118 S. aureus isolates, indicating that nearly 10% of the Belgian farms suffering from S. aureus mastitis have an MRSA problem. The in-herd prevalence varied between 0% and 7.4%. Characterization of the MRSA strains showed that they were all resistant to tetracycline. Additional resistances to macrolides, lincosamides and aminoglycosides were frequently detected. The strains were ST398, spa-types t011 or t567 and had SCCmec-type IVa or V, proving that they belong to the emerging livestock-associated MRSA (LA-MRSA) strains of CC398. Our study shows that after detection in Belgian pigs, horses and poultry, LA-MRSA has also attained Belgian cattle. It is the first report on frequent isolation of LA-MRSA from bovine infections. As the in-herd isolation rate resembles that of regular S. aureus in farms experiencing S. aureus mastitis, the multi-resistance of LA-MRSA strains may cause future treatment problems.

Reclassification of Staphylococcus aureus nasal carriage types.

BACKGROUND: Persistent nasal carriers have an increased risk of Staphylococcus aureus infection, whereas intermittent carriers and noncarriers share the same low risk. This study was performed to provide additional insight into staphylococcal carriage types. METHODS: Fifty-one volunteers who had been decolonized with mupirocin treatment and whose carriage state was known were colonized artificially with a mixture of S. aureus strains, and intranasal survival of S. aureus was compared between carriage groups. Antistaphylococcal antibody levels were also compared among 83 carriage-classified volunteers. RESULTS: Persistent carriers preferentially reselected their autologous strain from the inoculum mixture (P=.02). They could be distinguished from intermittent carriers and noncarriers on the basis of the duration of postinoculation carriage (154 vs. 14 and 4 days, respectively; P=.017, by log-rank test). Cultures of swab samples from persistent carriers contained significantly more colony-forming units per sample than did cultures of swab samples from intermittent carriers and noncarriers (P=.004). Analysis of serum samples showed that levels of immunoglobulin G and immunoglobulin A to 17 S. aureus antigens were equal in intermittent carriers and noncarriers but not in persistent carriers. CONCLUSIONS: Along with the previously described low risk of infection, intermittent carriers and noncarriers share similar S. aureus nasal elimination kinetics and antistaphylococcal antibody profiles. This implies a paradigm shift; apparently, there are only 2 types of nasal carriers: persistent carriers and others. This knowledge may increase our understanding of susceptibility to S. aureus infection.