Fathollah Riahi

Pneumococcal serotypes before and after introduction of conjugate vaccines, United States, 1999-2011(1.).

Serotyping data for pneumococci causing invasive and noninvasive disease in 2008–2009 and 2010–2011 from >43 US centers were compared with data from preconjugate vaccine (1999–2000) and postconjugate vaccine (2004–2005) periods. Prevalence of 7-valent pneumococcal conjugate vaccine serotypes decreased from 64% of invasive and 50% of noninvasive isolates in 1999–2000 to 3.8% and 4.2%, respectively, in 2010–2011. Increases in serotype 19A stopped after introduction of 13-valent pneumococcal vaccine (PCV13) in 2010. Prevalences of other predominant serotypes included in or related to PCV13 (3, 6C, 7F) also remained similar for 2008–2009 and 2010–2011. The only major serotype that increased from 2008–2009 to 2010–2011 was nonvaccine serotype 35B. These data show that introduction of the 7-valent vaccine has dramatically decreased prevalence of its serotypes and that addition of serotypes in PCV13 could provide coverage of 39% of isolates that continue to cause disease.

Changing Epidemiology of Antimicrobial-Resistant Streptococcus pneumoniae in the United States, 2004–2005

BACKGROUND The impact of pediatric 7-valent pneumococcal conjugate vaccination (PCV-7) on the population of Streptococcus pneumoniae in the United States was examined by determining the serotypes, antimicrobial resistance profiles, and genetic relatedness of isolates from patients with invasive and noninvasive infections during the 2004-2005 respiratory illness season. METHODS Susceptibility testing, serotyping, and pulsed-field gel electrophoresis analysis were performed on 1647 S. pneumoniae isolates obtained from 41 US medical centers in 2004-2005 as part of a longitudinal antimicrobial resistance surveillance program. The results were compared with surveillance data from earlier periods. RESULTS From the 1999-2000 to the 2004-2005 respiratory illness season, the prevalence of isolates with intermediate penicillin resistance (minimum inhibitory concentration, 0.1-1 microg/mL) increased from 12.7% to 17.9%, prevalence of penicillin-resistant isolates (minimum inhibitory concentration, >or=2 microg/mL) decreased from 21.5% to 14.6%, and prevalence of isolates resistant to erythromycin increased from 25.7% to 29.1% among S. pneumoniae isolates. The prevalence of multidrug resistance among isolates did not change (22.4% in 1999-2000 and 20.0% in 2004-2005). Sixty different serotypes were recognized among the isolates from 2004-2005; predominant serotypes were 19A (14.5%), 3 (11.2%), 6A (7.1%), 19F (7%), and 11A (6%). Serotypes that were included in PCV-7 accounted for 16.3% of isolates; 28.4% of strains isolated had PCV-7-related serotypes, and the remaining 55.3% of isolates had serotypes that were unrelated to PCV-7. The serotype distribution of the penicillin-resistant S. pneumoniae population changed from 1999-2000 to 2004-2005, with an increase in the prevalence of serotype 19A (1.5% to 35.4%) and serotype 35B (1.2% to 12.5%) and a decrease in the prevalence of most PCV-7 serotypes, including 23F (16.1% to 5%), 9V (16.1% to 4.2%), 6B (13.7% to 3.8%), and 14 (18.5% to 2.9%). CONCLUSIONS The penicillin-resistant S. pneumoniae population has changed; most isolates are now closely related to 2 Pneumococcal Molecular Epidemiology Network clones that increased in prevalence from 1999-2000 to 2004-2005 (Taiwan(19F)-14 [14.6% to 36.7%; 60% were serotype 19A] and Utah(35B)-24 [0.9% to 16.3%]).

Changes in Pneumococcal Serotypes and Antimicrobial Resistance after Introduction of the 13-Valent Conjugate Vaccine in the United States

ABSTRACT Ongoing surveillance for Streptococcus pneumoniae is needed to assess the impact of the pneumococcal conjugate vaccine introduced in 2010 (PCV13). Forty-two U.S. centers submitted S. pneumoniae isolates between 1 October 2012 and 31 March 2013. Susceptibility testing was performed by use of a broth dilution method as recommended by the Clinical and Laboratory Standards Institute. Serotyping was performed by multiplex PCR and the Quellung reaction. Multidrug resistance (MDR) was defined as nonsusceptibility to penicillin (PNSP; MIC ≥ 0.12 μg/ml) combined with resistance to ≥2 non-β-lactam antimicrobials. Penicillin-resistant S. pneumoniae (PRSP) was defined as a penicillin MIC of ≥2 μg/ml. For the 1,498 isolates collected during 2012-13, the PRSP and MDR rates were 14.2 and 21.0%, respectively. These percentages were lower than rates obtained in a surveillance study conducted 4 years earlier in 2008-09 (17.0 and 26.6%, respectively). The most common serotypes identified in 2012-13 were 3, 35B, and 19A, each representing 9 to 10% of all isolates. The largest percentage of PNSP in 2012-13 were found in serotypes 35B (24.8%), 19A (23.5%), and 15A (10.3%). Predominant PRSP serotypes were 19A (54.5%), 35B (28.2%), and 19F (7.0%). Major MDR serotypes were 19A (38.5%), 15A (16.9%), 6C (8.3%), and 35B (6.4%). The change in prevalence of PCV13 serotypes (43.4 to 27.1%) was primarily due to a decrease in serotype 19A strains, i.e., 22% of all strains in 2008-09 to 10% of all strains in 2012-13. Among the PNSP subset, serotypes showing a proportional increase were 35B, 15B, and 23B. Among MDR strains, the largest proportional increases were observed in serotypes 35B, 15B, and 23A.

Continued Emergence of USA300 Methicillin-Resistant Staphylococcus aureus in the United States: Results from a Nationwide Surveillance Study

BACKGROUND The epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) is changing, with USA300 emerging first in community and then in healthcare settings. We performed nationwide surveillance to assess recent trends in the molecular epidemiology of MRSA. METHODS One hundred consecutive unique clinically significant S. aureus isolates were recovered from patients at each of 43 US centers between July 1, 2011, and December 31, 2011. Susceptibility testing, pulsed-field gel electrophoresis (PFGE), staphylococcal protein A gene (spa) and staphylococcal cassette chromosome mec typing, and Panton-Valentine leukocidin detection were performed on all MRSA isolates. RESULTS Of 4,131 isolates collected, 2,093 (51%) were MRSA. Specimen sources of MRSA isolates included wound or abscess (54%), blood (24%), lower respiratory tract (11%), and other sterile site (10%). Thirty percent were isolated more than 48 hours after hospital admission (ie, were associated with nosocomial acquisition of infection). USA300 was the most common PFGE type (1,269 isolates; 61%), overall and in all regions, followed by USA100 (368 isolates; 18%). Among 173 spa types found, the most common were t008 (51%) and t002 (18%); no other spa type accounted for more than 2% of isolates. One strain type (USA300/t008/IV) constituted almost half of all MRSA isolates (1,005 isolates; 48%) and was the most common at all body sites, causing 37% of MRSA bloodstream infections (BSIs) and 38% of nosocomial MRSA infections. Multidrug-resistant phenotypes were found among 34 USA300 isolates (3%) from 18 states. CONCLUSIONS The USA300 PFGE type continues to advance nationwide. A single strain type (USA300/t008/IV) predominates in all regions and infection sites and is now more common than USA100 as a cause of MRSA BSI and nosocomial infections. Although most USA300 retain typical susceptibility profiles, multidrug-resistant phenotypes are emerging.

Activity of Ceftaroline and Epidemiologic Trends in Staphylococcus aureus Isolates Collected from 43 Medical Centers in the United States in 2009

ABSTRACT A Staphylococcus aureus surveillance program was initiated in the United States to examine the in vitro activity of ceftaroline and epidemiologic trends. Susceptibility testing by Clinical and Laboratory Standards Institute broth microdilution was performed on 4,210 clinically significant isolates collected in 2009 from 43 medical centers. All isolates were screened for mecA by PCR and evaluated by pulsed-field gel electrophoresis. Methicillin-resistant S. aureus (MRSA) were analyzed for Panton-Valentine leukocidin (PVL) genes and the staphylococcal cassette chromosome mec (SCCmec) type. All isolates had ceftaroline MICs of ≤2 μg/ml with an MIC50 of 0.5 and an MIC90 of 1 μg/ml. The overall resistance rates, expressed as the percentages of isolates that were intermediate and resistant (or nonsusceptible), were as follows: ceftaroline, 1.0%; clindamycin, 30.2% (17.4% MIC ≥ 4 μg/ml; 12.8% inducible); daptomycin, 0.2%; erythromycin, 65.5%; levofloxacin, 39.9%; linezolid, 0.02%; oxacillin, 53.4%; tetracycline, 4.4%; tigecycline, 0%; trimethoprim-sulfamethoxazole, 1.6%; vancomycin, 0%; and high-level mupirocin, 2.2%. The mecA PCR was positive for 53.4% of the isolates. The ceftaroline MIC90s were 0.25 μg/ml for methicillin-susceptible S. aureus and 1 μg/ml for MRSA. Among the 2,247 MRSA isolates, 51% were USA300 (96.9% PVL positive, 99.7% SCCmec type IV) and 17% were USA100 (93.4% SCCmec type II). The resistance rates for the 1,137 USA300 MRSA isolates were as follows: erythromycin, 90.9%; levofloxacin, 49.1%; clindamycin, 7.6% (6.2% MIC ≥ 4 μg/ml; 1.4% inducible); tetracycline, 3.3%; trimethoprim-sulfamethoxazole, 0.8%; high-level mupirocin, 2.7%; daptomycin, 0.4%; and ceftaroline and linezolid, 0%. USA300 is the dominant clone causing MRSA infections in the United States. Ceftaroline demonstrated potent in vitro activity against recent S. aureus clinical isolates, including MRSA, daptomycin-nonsusceptible, and linezolid-resistant strains.

Detection of Staphylococcus aureus Isolates with Heterogeneous Intermediate-Level Resistance to Vancomycin in the United States

ABSTRACT The prevalence of heterogeneous intermediate-level resistance to vancomycin (hVISA) in Staphylococcus aureus was assessed by screening a large collection of recent isolates. Susceptibility testing by the Clinical and Laboratory Standards Institute broth microdilution method and the Etest GRD (glycopeptide resistance detection) method (bioMérieux) was performed on 4,210 clinically significant S. aureus isolates obtained in 2009 from 43 U.S. centers. Isolates with Etest GRD-positive results for hVISA were evaluated further by repeat GRD testing and population analysis profiling–area under the curve (PAP-AUC) analysis. No VISA (vancomycin MIC, 4 to 8 μg/ml) or vancomycin-resistant (MIC ≥ 16 μg/ml) strains were detected. The Etest GRD screen for hVISA was initially positive for 68 isolates (1.6%; all by teicoplanin MIC ≥ 8 μg/ml at 24 or 48 h). Among those 68 isolates, 45 were reproducibly GRD positive. PAP-AUC testing confirmed only 11 isolates as hVISA (all had reproducible GRD-positive results). The 11 hVISA isolates were from nine medical centers and appeared genetically diverse (ten different PFGE types). The rates of resistance (including intermediate) for hVISA were as follows: oxacillin, 82%; erythromycin, 82%; clindamycin, 73%; levofloxacin, 73%; trimethoprim-sulfamethoxazole, 9%; and daptomycin, 9%. All hVISA isolates were susceptible to linezolid, tigecycline, and ceftaroline. Our data suggest that the overall prevalence of hVISA in the United States is low (0.3%). The hVISA isolates represented 10.5% of isolates with vancomycin MICs of 2 μg/ml and 0.1% of isolates with vancomycin MICs of 1 μg/ml. The positive predictive value of GRD Etest for hVISA was 16.2% for initial screen positive and 24.4% for reproducibly positive results.

Accuracy of Phenotypic Methods for Identification of Streptococcus pneumoniae Isolates Included in Surveillance Programs

ABSTRACT Similarities between Streptococcus pneumoniae and viridans group streptococci may result in misidentification of these organisms. In surveillance programs which assess antimicrobial resistance rates among respiratory tract pathogens, such identification errors could lead to overestimates of pneumococcal resistance rates. DNA probe analysis (Gen-Probe, San Diego, CA), the bile solubility test, optochin susceptibility, colony morphology, and the capsular swelling reaction with Omni serum (Staten Serum Institut, Copenhagen, Denmark) were used to characterize 1,733 organisms provisionally identified as S. pneumoniae in a 2004 to 2005 antimicrobial resistance surveillance program. These organisms were obtained in 41 U.S. medical centers. Among these, 1,647 (95%) were determined to be S. pneumoniae by DNA probe. Elimination of those isolates found not to be S. pneumoniae resulted in 1 to 2% decreases in resistance rate estimates with penicillin, erythromycin, tetracycline, and trimethoprim-sulfamethoxazole. With AccuProbe as a reference standard, the sensitivities and specificities of each phenotypic method for the identification of S. pneumoniae were, respectively, 98.8% and 82.6% for bile solubility, 99.3% and 74.4% for the capsular swelling reaction with Omni serum, and 87.9% and 59.3% for optochin susceptibility. Colony morphology was of limited value, as 391 (23.7%) isolates lacked the typical button or mucoid colony appearance of S. pneumoniae.

Increasing telithromycin resistance among Streptococcus pyogenes in Europe

OBJECTIVES To assess changes in macrolide and ketolide resistance among Streptococcus pyogenes in Europe and to examine the relationship of resistance to antimicrobial usage. METHODS Clinical S. pyogenes isolates were collected from Denmark, Finland, France, Germany, Italy, Netherlands, Norway, Spain, Sweden, UK, Croatia, Hungary, Poland, Slovak Republic and Slovenia during 2002-03 (n = 2165) and 2004-05 (n = 2333). Resistance to telithromycin (MIC > or = 2) and erythromycin (MIC > or = 0.5) was determined by CLSI broth microdilution. Changes in resistance over time and the relationship of resistance to antimicrobial use (European Surveillance of Antimicrobial Consumption data) were assessed. Telithromycin-resistant isolates were characterized by PFGE to determine genetic relatedness and by PCR to detect mef(A), erm(A) and erm(B). RESULTS The erythromycin resistance rate during 2004-05 (11.6%) was similar to 2002-03 (10.4%). The proportion of macrolide-resistant isolates with the constitutive MLS(B) phenotype increased from 29.3% (2002-03) to 45.7% (2004-05). Telithromycin resistance increased from 1.8% in 2002-03 to 5.2% in 2004-05. For Western Europe, associations of telithromycin and erythromycin resistance, respectively, were found with azithromycin use (R2 = 0.52 and 0.60), clarithromycin use (R2 = 0.76 and 0.85) and total macrolide/lincosamide use (R2 = 0.75 and 0.69). For Eastern Europe, associations of antimicrobial use with resistance were not apparent. The 162 telithromycin-resistant isolates comprised 42 PFGE patterns with 68.5% in eight major PFGE groups. The erm(B) gene was detected in 155 of the 162 telithromycin-resistant isolates. CONCLUSIONS Significant increases in telithromycin resistance occurred from 2002-03 to 2004-05 in Europe. Macrolide use appears to be a factor in the emergence of ketolide resistance among S. pyogenes in Western Europe.

Activities of Vancomycin, Ceftaroline, and Mupirocin against Staphylococcus aureus Isolates Collected in a 2011 National Surveillance Study in the United States

ABSTRACT Forty-two medical centers from throughout the United States participating in a longitudinal surveillance program were asked to submit 100 consecutive Staphylococcus aureus isolates during July to December 2011. Susceptibility testing using CLSI broth microdilution and mecA detection by PCR analysis was performed on the 4,131 isolates collected. Methods employing Etest glycopeptide resistance detection (GRD; bioMérieux) and brain heart infusion agar containing 4 μg/ml vancomycin (BHIV) were used to screen methicillin-resistant S. aureus (MRSA) isolates for heterogeneous intermediate-level resistance to vancomycin (hVISA). Isolates with positive hVISA screen results were confirmed by population analysis profiling-area under the curve (PAP-AUC) determinations. The genetic relatedness of hVISA, ceftaroline-nonsusceptible, or high-level (HL) mupirocin resistance MRSA isolates was assessed by pulsed-field gel electrophoresis (PFGE). Among 2,093 MRSA isolates, the hVISA screen results were positive with 47 isolates by Etest GRD and 30 isolates by BHIV agar screen. Twenty-five of the GRD- or BHIV screen-positive isolates were confirmed as hVISA by PAP-AUC testing. Results of the current study were compared to results obtained from prior surveillance performed in 2009. The prevalence of hVISA among MRSA isolates was higher in 2011 than in 2009 (1.2% versus 0.4%, P = 0.003), especially for isolates with a vancomycin MIC of 2 (45.4% versus 14.3%, P = 0.01). The overall rate of ceftaroline susceptibility in the current study was 99.4% (one hVISA isolate had an intermediate ceftaroline MIC). HL mupirocin resistance increased from 2.2% in 2009 to 3.2% in 2011 (P = 0.006). Although overall rates of hVISA and HL mupirocin resistance are low, they have increased since 2009.

Evaluation of Pneumococcal Serotyping by Multiplex PCR and Quellung Reactions

ABSTRACT Screening of 1,750 pneumococcal isolates for common serotypes by PCR was followed by Quellung reaction analysis of PCR-negative isolates with a comparison to the conventional (Quellung reaction only) approach. PCR agreed with Quellung reaction results for 99% of isolates. The sequential PCR/Quellung reaction algorithm is accurate and more cost-effective than the conventional approach.