Gregory E. Fosheim

Changes in the Prevalence of Nasal Colonization with Staphylococcus aureus in the United States, 2001–2004

BACKGROUND Staphylococcus aureus is a common cause of infection, particularly in persons colonized by this organism. Virulent strains of methicillin-resistant S. aureus (MRSA) have emerged in the general community. METHODS A nationally representative survey of nasal colonization with S. aureus was conducted from 2001 through 2004 as part of the National Health and Nutrition Examination Survey. MRSA isolates were identified by the oxacillin disk-diffusion method. The pulsed-field gel electrophoresis (PFGE) type was determined for all MRSA isolates. A t statistic was used to compare the prevalence of colonization across biennia and across population subgroups. Cofactors independently associated with colonization were determined with backward stepwise logistic modeling. RESULTS The prevalence of colonization with S. aureus decreased from 32.4% in 2001-2002 to 28.6% in 2003-2004 (P < .01), whereas the prevalence of colonization with MRSA increased from 0.8% to 1.5% (P < .05). Colonization with MRSA was independently associated with healthcare exposure in males and with having been born in the United States, age > or =60 years, diabetes, and poverty in females. In 2003-2004, a total of 19.7% (95% confidence interval, 12.4%-28.8%) of MRSA-colonized persons carried a PFGE type associated with community transmission. CONCLUSIONS Nasal colonization with MRSA has increased in the United States, despite an overall decrease in nasal colonization with S. aureus. PFGE types associated with community transmission only partially account for the increase in MRSA colonization.

Prevalence of Staphylococcus aureus Nasal Colonization in the United States, 2001–2002

BACKGROUND Staphylococcus aureus is a common cause of disease, particularly in colonized persons. Although methicillin-resistant S. aureus (MRSA) infection has become increasingly reported, population-based S. aureus and MRSA colonization estimates are lacking. METHODS Nasal samples for S. aureus culture and sociodemographic data were obtained from 9622 persons > or = 1 year old as part of the National Health and Nutrition Examination Survey, 2001-2002. After screening for oxacillin susceptibility, MRSA and selected methicillin-susceptible S. aureus isolates were tested for antimicrobial susceptibility, pulsed-field gel electrophoresis clonal type, toxin genes (e.g., for Panton-Valentine leukocidin [PVL]), and staphylococcal cassette chromosome mec (SCCmec) type I-IV genes. RESULTS For 2001-2002, national S. aureus and MRSA colonization prevalence estimates were 32.4% (95% confidence interval [CI], 30.7%-34.1%) and 0.8% (95% CI, 0.4%-1.4%), respectively, and population estimates were 89.4 million persons (95% CI, 84.8-94.1 million persons) and 2.3 million persons (95% CI, 1.2-3.8 million persons), respectively. S. aureus colonization prevalence was highest in participants 6-11 years old. MRSA colonization was associated with age > or = 60 years and being female but not with recent health-care exposure. In unweighted analyses, the SCCmec type IV gene was more frequent in isolates from participants of younger age and of non-Hispanic black race/ethnicity; the PVL gene was present in 9 (2.4%) of 372 of isolates tested. CONCLUSIONS Many persons in the United States are colonized with S. aureus; prevalence rates differ demographically. MRSA colonization prevalence, although low nationally in 2001-2002, may vary with demographic and organism characteristics.

Severe community-acquired pneumonia due to Staphylococcus aureus, 2003-04 influenza season

S. aureus community-acquired pneumonia has been reported from 9 states.

Comparison of Staphylococcus aureus From Skin and Soft-Tissue Infections in US Emergency Department Patients, 2004 and 2008

BACKGROUND In the past decade, new methicillin-resistant Staphylococcus aureus (MRSA) strains have emerged as a predominant cause of community-associated skin and soft-tissue infections (SSTIs). Little information exists regarding trends in MRSA prevalence and molecular characteristics or regarding antimicrobial susceptibility profiles of S. aureus isolates. METHODS We enrolled adults with acute, purulent SSTIs presenting to a US network of 12 emergency departments during August 2008. Cultures and clinical information were collected. S. aureus isolates were characterized by antimicrobial susceptibility testing, pulsed-field gel electrophoresis, and toxin genes detection. The prevalence of S. aureus and MRSA and isolate genetic characteristics and susceptibilities were compared with those from a similar study conducted in August 2004. RESULTS The prevalence of MRSA was 59% among all SSTIs during both study periods; however, the prevalence by site varied less in 2008 (38%-84%), compared with 2004 (15%-74%). Pulsed-field type USA300 continued to account for almost all MRSA isolates (98%). Susceptibility to trimethoprim-sulfamethoxazole, clindamycin, and tetracycline among MRSA isolates remained greater than 90% in 2008. A higher proportion of MRSA infections were treated with an agent to which the infecting isolate was susceptible in vitro in 2008 (97%), compared with 2004 (57%). CONCLUSIONS Similar to 2004, MRSA remained the most common identifiable cause of purulent SSTIs among patients presenting to a network of US emergency departments in 2008. The infecting MRSA isolates continued to be predominantly pulsed-field type USA300 and susceptible to recommended non-β-lactam oral agents. Clinician prescribing practices have shifted from MRSA-inactive to MRSA-active empirical antimicrobial regimens.

Emergence of Resistance among USA300 Methicillin-Resistant Staphylococcus aureus Isolates Causing Invasive Disease in the United States

ABSTRACT USA300 methicillin-resistant Staphylococcus aureus (MRSA) isolates are usually resistant only to oxacillin, erythromycin, and, increasingly, levofloxacin. Of these, oxacillin and levofloxacin resistances are chromosomally encoded. Plasmid-mediated clindamycin, mupirocin, and/or tetracycline resistance has been observed among USA300 isolates, but these descriptions were limited to specific patient populations or isolated occurrences. We examined the antimicrobial susceptibilities of invasive MRSA isolates from a national surveillance population in order to identify USA300 isolates with unusual, possibly emerging, plasmid-mediated antimicrobial resistance. DNA from these isolates was assayed for the presence of resistance determinants and the presence of a pSK41-like conjugative plasmid. Of 823 USA300 isolates, 72 (9%) were tetracycline resistant; 69 of these were doxycycline susceptible and tetK positive, and 3 were doxycycline resistant and tetM positive. Fifty-one (6.2%) isolates were clindamycin resistant and ermC positive; 22 (2.7%) isolates were high-level mupirocin resistant (mupA positive); 5 (0.6%) isolates were trimethoprim-sulfamethoxazole (TMP-SMZ) resistant, of which 4 were dfrA positive; and 7 (0.9%) isolates were gentamicin resistant and aac6′-aph2″ positive. Isolates with pSK41-like plasmids (n = 24) were positive for mupA (n = 19), dfrA (n = 6), aac6′-aph2″ (n = 6), tetM (n = 2), and ermC (n = 8); 20 pSK41-positive isolates were positive for two or more resistance genes. Conjugative transfer of resistance was demonstrated between four gentamicin- and mupirocin-resistant and three gentamicin- and TMP-SMZ-resistant USA300 isolates; transconjugants harbored a single pSK41-like plasmid, which was PCR positive for aac6′-aph2″ and either mupA and/or dfrA. USA300 and USA100 isolates from the same state with identical resistance profiles contained pSK41-like plasmids with indistinguishable restriction and Southern blot profiles, suggesting horizontal plasmid transfer between USA100 and USA300 isolates.

Staphylococcus aureus Community-Acquired Pneumonia During the 2006 to 2007 Influenza Season

STUDY OBJECTIVE Staphylococcus aureus is a cause of community-acquired pneumonia that can follow influenza infection. In response to a number of cases reported to public health authorities in early 2007, additional case reports were solicited nationwide to better define S. aureus community-acquired pneumonia during the 2006 to 2007 influenza season. METHODS Cases were defined as primary community-acquired pneumonia caused by S. aureus occurring between November 1, 2006, and April 30, 2007. Case finding was conducted through an Emerging Infections Network survey and through contacts with state and local health departments. RESULTS Overall, 51 cases were reported from 19 states; 37 (79%) of 47 with known susceptibilities involved infection with methicillin-resistant S. aureus (MRSA). The median age of case patients was 16 years, and 44% had no known pertinent medical history. Twenty-two (47%) of 47 case patients with information about other illnesses were diagnosed with a concurrent or antecedent viral infection during their illness, and 11 of 33 (33%) who were tested had laboratory-confirmed influenza. Of the 37 patients with MRSA infection, 16 (43%) were empirically treated with antimicrobial agents recommended for MRSA community-acquired pneumonia. Twenty-four (51%) of 47 patients for whom final disposition was known died a median of 4 days after symptom onset. CONCLUSION S. aureus continues to cause community-acquired pneumonia, with most reported cases caused by MRSA and many occurring with or after influenza. In this series, patients were often otherwise healthy young people and mortality rates were high. Further prospective investigation is warranted to clarify infection incidence, risk factors, and preventive measures.

Characterization of Methicillin-Resistant Staphylococcus aureus Isolates Collected in 2005 and 2006 from Patients with Invasive Disease: a Population-Based Analysis

ABSTRACT This study characterizes 1,984 methicillin-resistant Staphylococcus aureus (MRSA) isolates collected in 2005 and 2006 from normally sterile sites in patients with invasive MRSA infection. These isolates represent a convenience sample of all invasive MRSA cases reported as part of the Active Bacterial Core surveillance system in eight states in the United States. The majority of isolates were from blood (83.8%), joints (4.1%), and bone (4.2%). Isolates were characterized by pulsed-field gel electrophoresis (PFGE); SCCmec typing; susceptibility to 15 antimicrobial agents; and PCR analysis of staphylococcal enterotoxin A (SEA) to SEH, toxic shock syndrome toxin 1, and Panton-Valentine leukocidin. Thirteen established PFGE types were recognized among these isolates, although USA100 and USA300 predominated, accounting for 53.2% and 31.4% of the isolates, respectively. As expected, isolates from hospital onset cases were predominantly USA100, whereas those from community-associated cases were predominantly USA300. USA100 isolates were diverse (Simpsons discriminatory index [DI] = 0.924); generally positive only for enterotoxin D (74.5%); and resistant to clindamycin (98.6%), erythromycin (99.0%), and levofloxacin (99.6%), in addition to β-lactam agents. USA300 isolates were less diverse (DI = 0.566), positive for Panton-Valentine leukocidin (96.3%), and resistant to erythromycin (94.1%) and, less commonly, levofloxacin (54.6%), in addition to β-lactam agents. This collection provides a reference collection of MRSA isolates associated with invasive disease, collected in 2005 and 2006 in the United States, for future comparison and ongoing studies.

Characterization of Staphylococcus aureus Isolates from Nasal Cultures Collected from Individuals in the United States in 2001 to 2004

ABSTRACT This study characterizes methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA) isolates recovered from nasal cultures of noninstitutionalized individuals in the United States obtained in 2001 to 2004 as part of the National Health and Nutrition Examination Survey. Every tenth MSSA isolate and all MRSA isolates were typed by pulsed-field gel electrophoresis (PFGE), screened for multiple toxin genes, and tested for susceptibility to 14 antimicrobial agents. USA200, USA600, and USA900 were the predominant PFGE types among MSSA isolates in both the 2001 to 2002 and the 2003 to 2004 time periods, although they accounted for only 51.3% of 316 MSSA isolates typed in 2001 and 2002 and only 43.4% of 237 MSSA isolates typed in 2003 and 2004. In contrast, USA100, USA800, and USA700 accounted for 80.0% of the 75 MRSA isolates typed in 2001 and 2002, while USA100, USA800, and USA300 accounted for 78.4% of 134 MRSA isolates typed in 2003 and 2004. The proportion of MRSA isolates that were USA300 increased significantly from the first to the second time period (P = 0.03). Most USA200 isolates (both MSSA and MRSA) carried the gene for toxic shock syndrome toxin; however, carriage of the genes encoding Panton-Valentine leukocidin, while common among MRSA of PFGE type USA300, was rare among MSSA USA300 in both time periods. Most MSSA isolates remained susceptible to all antimicrobial agents except erythromycin (79.1 and 76.0% susceptibilities in the 2001 to 2002 and the 2003 to 2004 periods, respectively). In contrast, the proportions of MRSA isolates that were susceptible to chloramphenicol, clindamycin, and erythromycin were lower in 2003 and 2004 than in 2001 and 2002, although none of these differences was statistically significant.

Multiple-Locus Variable-Number Tandem-Repeat Assay Analysis of Methicillin-Resistant Staphylococcus aureus Strains

ABSTRACT Our objective was to determine if a multiple-locus variable-number tandem-repeat assay (MLVA) for Staphylococcus aureus could predict pulsed-field gel electrophoresis (PFGE) types (i.e., USA types), thus allowing us to replace PFGE with a simpler and more rapid typing method. One hundred three well-characterized isolates representing 13 major lineages of S. aureus were tested by both PFGE and MLVA. MLVA was performed using a rapid DNA extraction technique and PCR primers for sdrCDE, clfA, clfB, sspA, and spa. PFGE was performed with genomic DNA fragments generated using SmaI, as per CDC protocols. Banding patterns were analyzed both visually and with BioNumerics software. All isolates were typeable with MLVA and PFGE. MLVA patterns were highly reproducible. PFGE separated the isolates into 13 types with 42 subtypes. Using any band difference to designate a novel MLVA type, MLVA produced 45 types, including 9 clusters containing multiple isolates. Using BioNumerics and a cutoff of >75% relatedness, MLVA produced 28 types, 11 of which contained >1 isolate. Epidemiologically related outbreak isolates of USA300-0114 from five states clustered in one MLVA pattern. USA100 isolates were present in several unrelated (<40%) MLVA types. A cutoff of >80% separated outbreak strains of USA300-0114 into three distinct MLVA types. MLVA did not differentiate community methicillin-resistant S. aureus (MRSA) lineages (USA300, USA400, USA1000, and USA1100) from health care MRSA lineages (USA100, USA200, or USA500). The ability of MLVA to differentiate among strains that are indistinguishable by PFGE may be of epidemiologic value and warrants further study.

Methamphetamine Use and Methicillin-Resistant Staphylococcus aureus Skin Infections

Drug use may be contributing to the spread of MRSA in a rural southeastern US community.