Epidemiological and molecular characterization of Streptococcus pneumoniae carriage strains in pre-school children in Arkhangelsk, northern European Russia, prior to the introduction of conjugate pneumococcal vaccines.

BACKGROUND: The 13-valent Pneumococcal Conjugate Vaccine (PCV-13) was introduced in the National Immunization Programme (NIP) schedule in Russia in March 2014. Previously, the 7-valent Pneumococcal Conjugate Vaccine (PCV-7) was marketed in Russia in 2009 but has never been offered for mass vaccination. A carriage study was performed among children in Arkhangelsk in 2006. The objective was to determine the prevalence of carriage, serotype distribution, antimicrobial susceptibility and the molecular structure of Streptococcus pneumoniae strains before marketing and introduction of PCV-13. METHODS: A cross-sectional study was conducted on a cluster-randomized sample of children and a self-administrated questionnaire for parents/guardians.  Nasopharyngeal samples were collected from 438 children younger than 7 years attending nurseries and kindergartens in the Arkhangelsk region, Russia. Detailed demographic data, as well as information about the child's health, traveling, exposure to antimicrobials within the last 3 months and anthropometric measurements were collected for all study subjects. Variables extracted from the questionnaire were analysed using statistic regression models to estimate the risk of carriage. All pneumococcal  isolates were examined with susceptibility testing, serotyping and multilocus sequence typing. RESULTS: The overall prevalence of asymptomatic carriage was high and peaking at 36 months with a rate of 57%. PCV-13 covered 67.3% of the detected strains. High rates of non-susceptibility to penicillin, macrolides and multidrug resistance were associated with specific vaccine serotypes, pandemic clones, and local sequence types. Nine percent of isolates represented three globally disseminated disease-associated pandemic clones; penicillin- and macrolide-resistant clones NorwayNT-42 and Poland6B-20, as well as penicillin- and macrolide-susceptible clone Netherlands3-31. A high level of antimicrobial consumption was noted by the study. According to the parent's reports, 89.5% of the children used at least one antimicrobial regime since birth. None of the hypothesised predictors of S. pneumoniae carriage were statistically significant in univariable and multivariable logistic models. CONCLUSIONS: The study identified a high coverage of the PCV-13-vaccine, but serotype replacement and expansion of globally disseminated disease-associated clones with non-vaccine serotypes may be expected. Further surveillance of antimicrobial resistance and serotype distribution is therefore required.

Meningococcal carriage in Norwegian teenagers: strain characterisation and assessment of risk factors.

Teenagers have a higher risk of invasive meningococcal disease (IMD) than the general population. This cross-sectional study aimed to characterise strains of Neisseria meningitidis circulating among Norwegian teenagers and to assess risk factors for meningococcal carriage. Oropharyngeal swabs were collected from secondary-school students in southeastern Norway in 2018-2019. Meningococcal isolates were characterised using whole genome sequencing. Risk factors for meningococcal carriage were assessed from questionnaire data. Samples were obtained from 2296 12-24-year-olds (majority 13-19-year-olds). N. meningitidis was identified in 167 (7.3%) individuals. The highest carriage rate was found among 18-year-olds (16.4%). Most carriage isolates were capsule null (40.1%) or genogroup Y (33.5%). Clonal complexes cc23 (35.9%) and cc198 (32.3%) dominated and 38.9% of carriage strains were similar to invasive strains currently causing IMD in Norway. Use of Swedish snus (smokeless tobacco) (OR 1.56, 95% CI 1.07-2.27), kissing >two persons/month (OR 2.76, 95% CI 1.49-5.10) and partying >10 times/3months (OR 3.50, 95% CI 1.45-8.48) were associated with carriage, while age, cigarette smoking, sharing of drinking bottles and meningococcal vaccination were not. The high meningococcal carriage rate among 18-year-olds is probably due to risk-related behaviour. Use of Swedish snus is possibly a new risk factor for meningococcal carriage. Almost 40% of circulating carriage strains have invasive potential.

Epidemiology of invasive group A streptococcal infections in Norway 2010-2014: A retrospective cohort study.

Streptococcus pyogenes or group A streptococcus (GAS) causes mild to severe infections in humans. GAS genotype emm1 is the leading cause of invasive disease worldwide. In the Nordic countries emm28 has been the dominant type since the 1980s. Recently, a resurgence of genotype emm1 was reported from Sweden. Here we present the epidemiology of invasive GAS (iGAS) infections and their association with emm-types in Norway from 2010-2014. We retrospectively collected surveillance data on antimicrobial susceptibility, multilocus sequence type and emm-type, and linked them with demographic and clinical manifestation data to calculate age and sex distributions, major emm- and sequence types and prevalence ratios (PR) on associations between emm-types and clinical manifestations. We analysed 756 iGAS cases and corresponding isolates, with overall incidence of 3.0 per 100000, median age of 59 years (range, 0-102), and male 56 %. Most frequent clinical manifestation was sepsis (49 %) followed by necrotizing fasciitis (9 %). Fifty-two different emm-types and 67 sequence types were identified, distributed into five evolutionary clusters. The most prevalent genotype was emm1 (ST28) in all years (range, 20-33 %) followed by 15 % emm28 in 2014. All isolates were susceptible to penicillin, 15 % resistant to tetracycline and <4 % resistant to erythromycin. A PR of 4.5 (95 % CI, 2.3-8.9) was calculated for emm2 and necrotizing fasciitis. All emm22 isolates were resistant to tetracycline PR 7.5 (95 % CI, 5.8-9.9). This study documented the dominance of emm1, emergence of emm89 and probable import of tetracycline resistant emm112.2 into Norway (2010-2014). Genotype fluctuations between years suggested a mutual exclusive dominance of evolutionary clades.

Salivary and Serum Antibody Response Against Neisseria meningitidis After Vaccination With Conjugate Polysaccharide Vaccines in Ethiopian Volunteers.

Meningococcal conjugate vaccines induce serum antibodies crucial for protection against invasive disease. Salivary antibodies are believed to be important for hindering meningococcal acquisition and/or clearance of established carriage. In this study, we measured salivary IgA and IgG antibodies induced by vaccination with a monovalent serogroup A conjugate vaccine or a tetravalent A, C, W and Y conjugate vaccine, in comparison with antibody levels in serum. Saliva and serum samples from Ethiopian volunteers (1-29 years) collected before and eight times on a weekly basis after receiving the serogroup A conjugate vaccine, the tetravalent serogroup A, C, W and Y conjugate vaccine, or no vaccine (control group), were analysed using a multiplex microsphere immunoassay for antibody detection. Serogroup-specific IgG antibody levels in saliva increased significantly after vaccination with both vaccines. The monovalent serogroup A vaccine also induced an increase in salivary IgA antibodies. A strong correlation between serogroup-specific IgG antibodies in saliva and serum, and a somewhat lower correlation for IgA, was observed for all serogroups. There was also a strong correlation between specific secretory IgA and IgA antibodies in saliva for all serogroups. Meningococcal conjugate vaccines are able to elicit salivary antibodies against serogroup A, C, W and Y correlating with antibody levels in serum. The strong correlation between saliva and serum antibody levels indicates that saliva may be used as a surrogate of systemic antibody responses.

Effect of a serogroup A meningococcal conjugate vaccine (PsA-TT) on serogroup A meningococcal meningitis and carriage in Chad: a community study [corrected].

BACKGROUND: A serogroup A meningococcal polysaccharide-tetanus toxoid conjugate vaccine (PsA-TT, MenAfriVac) was licensed in India in 2009, and pre-qualified by WHO in 2010, on the basis of its safety and immunogenicity. This vaccine is now being deployed across the African meningitis belt. We studied the effect of PsA-TT on meningococcal meningitis and carriage in Chad during a serogroup A meningococcal meningitis epidemic. METHODS: We obtained data for the incidence of meningitis before and after vaccination from national records between January, 2009, and June, 2012. In 2012, surveillance was enhanced in regions where vaccination with PsA-TT had been undertaken in 2011, and in one district where a reactive vaccination campaign in response to an outbreak of meningitis was undertaken. Meningococcal carriage was studied in an age-stratified sample of residents aged 1-29 years of a rural area roughly 13-15 and 2-4 months before and 4-6 months after vaccination. Meningococci obtained from cerebrospinal fluid or oropharyngeal swabs were characterised by conventional microbiological and molecular methods. FINDINGS: Roughly 1·8 million individuals aged 1-29 years received one dose of PsA-TT during a vaccination campaign in three regions of Chad in and around the capital N'Djamena during 10 days in December, 2011. The incidence of meningitis during the 2012 meningitis season in these three regions was 2·48 per 100,000 (57 cases in the 2·3 million population), whereas in regions without mass vaccination, incidence was 43·8 per 100,000 (3809 cases per 8·7 million population), a 94% difference in crude incidence (p<0·0001), and an incidence rate ratio of 0·096 (95% CI 0·046-0·198). Despite enhanced surveillance, no case of serogroup A meningococcal meningitis was reported in the three vaccinated regions. 32 serogroup A carriers were identified in 4278 age-stratified individuals (0·75%) living in a rural area near the capital 2-4 months before vaccination, whereas only one serogroup A meningococcus was isolated in 5001 people living in the same community 4-6 months after vaccination (adjusted odds ratio 0·019, 95% CI 0·002-0·138; p<0·0001). INTERPRETATION: PSA-TT was highly effective at prevention of serogroup A invasive meningococcal disease and carriage in Chad. How long this protection will persist needs to be established. FUNDING: The Bill & Melinda Gates Foundation, the Wellcome Trust, and Médecins Sans Frontères.

An outer membrane vesicle vaccine for prevention of serogroup A and W-135 meningococcal disease in the African meningitis belt.

The bacterium Neisseria meningitidis of serogroups A and W-135 has in the recent decade caused most of the cases of meningococcal meningitis in the African meningitis belt, and there is currently no efficient and affordable vaccine available demonstrated to protect against both these serogroups. Previously, deoxycholate-extracted outer membrane vesicle (OMV) vaccines against serogroup B meningococci have been shown to be safe and induce protection in humans in clonal outbreaks. The serogroup A and W-135 strains isolated from meningitis belt epidemics demonstrate strikingly limited variation in major surface-exposed protein structures. We have here investigated whether the OMV vaccine strategy also can be applied to prevent both serogroups A and W-135 meningococcal disease. A novel vaccine combining OMV extracted from recent African serogroup A and W-135 strains and adsorbed to aluminium hydroxide was developed and its antigenic characteristics and immunogenicity were studied in mice. The specificity of the antibody responses was analysed by immunoblotting and serum bactericidal activity (SBA) assays. Moreover, the bivalent A+W-135 vaccine was compared with monovalent A and W-135 OMV vaccines. The bivalent OMV vaccine was able to induce similar SBA titres as the monovalent A or W-135 OMV towards both serogroups. High SBA titres were also observed against a meningococcal serogroup C strain. These results show that subcapsular antigens may be of importance when developing broadly protective and affordable vaccines for the meningitis belt.

Similar superantigen gene profiles and superantigen activity in norwegian isolates of invasive and non-invasive group a streptococci.

Group A streptococcus (GAS) harbours several virulence factors, including M protein (coded by the emm gene) and superantigens (SAgs). SAgs are extracellular toxins that directly activate the immune system by cross-binding to the HLA class II molecule and T cell receptor (TCR), thereby causing activation of up to 30% of the T cells and subsequent massive secretion of cytokines. Forty-eight GAS strains isolated from patients at Norwegian hospitals between 1988 and 2004 were included in this study. Of these, 24 were invasive streptococcal toxic shock syndrome (STSS) or necrotizing fasciitis (NF) isolates and 24 were non-invasive pharyngitis isolates, matched for having the same T-type and year of isolation as the invasive isolates. The isolates were characterized by emm sequence typing, multilocus sequence typing (MLST) and SAg gene profiles. A correlation between T-type, emm type, sequence type and SAg gene profile was revealed. No difference between invasive and non-invasive isolates regarding serotype or genotype was demonstrated. Selected invasive and non-invasive isolates with identical SAg gene profiles were analysed for SAg activity in bacterial growth culture media with and without human cell culture media added. A human T cell proliferation assay was used as measurement for SAg activity and simultaneously we also measured the cytokine content in normal human peripheral blood leucocyte cell culture media. The results revealed that invasive and non-invasive isolates did not differ significantly in SAg activity as it is present in semipurified bacterial culture medium.

Avidity of serogroup A meningococcal IgG antibodies after immunization with different doses of a tetravalent A/C/Y/W135 polysaccharide vaccine.

In the absence of an affordable conjugate meningococcal vaccine, mass vaccination campaigns with polysaccharide vaccines are the means to control meningitis epidemics in sub-Saharan Africa. Facing global vaccine shortage, the use of reduced doses, which have been shown to be protective by serum bactericidal activity, can save many lives. In this study, we investigated the antibody responses and avidity of IgG antibodies evoked against the serogroup A capsule of Neisseria meningitidis by different doses of an A/C/Y/W135 polysaccharide vaccine. Volunteers in Uganda were vaccinated with 1/10, 1/5 or a full dose (50 µg) and revaccinated with a full dose after 1 year. Specific IgG geometric mean concentrations and geometric mean avidity indices (GMAI) were determined by a modified enzyme-linked immunosorbent assay (ELISA) using thiocyanate as a chaotropic agent. After vaccination with 1/10 or 1/5 doses, the GMAI increased from 1 month to 1 year. One year following the initial dose, the GMAI levels were higher in the arm receiving reduced doses than for the arm receiving a full dose. Following the second full dose, avidity indices equalized at approximately the same level in the three arms. Although there are practical challenges to the use of reduced doses in the field, our findings suggest that reduced doses of polysaccharide vaccine are able to elicit antibodies of as good avidity against serogroup A polysaccharide as a full dose.

Molecular characteristics of pharyngeal and invasive emm3 Streptococcus pyogenes strains from Norway, 1988-2003.

A major virulence factor of group A streptococci (GAS) is the M protein. Strains with the M3 type are more often associated with necrotizing fasciitis (NF) and streptococcal toxic shock syndrome, and have a higher case fatality rate than strains of other M types. To better understand the epidemiology of M3 GAS strains in Norway, we analyzed 59 invasive and 69 pharyngeal isolates with respect to prophage content, allelic variation in emm3, mtsR encoding the metal transporter of Streptococcus repressor (mtsR), and sclB coding for streptococcal collagen-like protein B. The Norwegian emm3 strains were very homogeneous, mainly harboring the emm allele 3.1 and prophage profile PhiG3.01. Other prophage profiles were transient. The mutation in mtsR known to truncate the protein and result in decreased capacity to cause NF was not found in our isolates. The sclB gene usually harbored five or eight contiguous repeats of a CAAAA pentanucleotide sequence and a highly modular and variable collagen structural motif (CSM) region with 9 and 12 amino acid M3-specific conserved motif repeats distributed across the entire CSM region. Strains with 5 CAAAA repeats emerged in 1993 and these strains were associated with the increase in invasive M3 cases in the period 1993-2003.

Meningococcal factor H-binding protein variants expressed by epidemic capsular group A, W-135, and X strains from Africa.

BACKGROUND: Meningococcal epidemics in Africa are generally caused by capsular group A strains, but W-135 or X strains also cause epidemics in this region. Factor H-binding protein (fHbp) is a novel antigen being investigated for use in group B vaccines. Little is known about fHbp in strains from other capsular groups. METHODS: We investigated fHbp in 35 group A, W-135, and X strains from Africa. RESULTS: The 22 group A isolates, which included each of the sequence types (STs) responsible for epidemics since 1963, and 4 group X and 3 group W-135 isolates from recent epidemics had genes encoding fHbp in antigenic variant group 1. The remaining 6 W-135 isolates had fHbp variant 2. Within each fHbp variant group, there was 92%-100% amino acid identity, and the proteins expressed conserved epitopes recognized by bactericidal monoclonal antibodies. Serum samples obtained from mice vaccinated with native outer membrane vesicle vaccines from mutants engineered to express fHbp variants had broad bactericidal activity against group A, W-135, or X strains. CONCLUSIONS: Despite extensive natural exposure of the African population, fHbp is conserved among African strains. A native outer membrane vesicle vaccine that expresses fHbp variants can potentially elicit protective antibodies against strains from all capsular groups that cause epidemics in the region.

Seroepidemiological study after a long-distance industrial outbreak of legionnaires' disease.

Following a long-distance outbreak of Legionnaires' disease from an industrial air scrubber in Norway in 2005, a seroepidemiological study measuring levels of immunoglobulin G (IgG) and IgM antibodies to Legionella pneumophila was performed with a polyvalent enzyme-linked immunosorbent assay. One year after the outbreak, IgG levels in employees (n = 213) at the industrial plant harboring the scrubber and in blood donors (n = 398) from the outbreak county were low but significantly higher (P < or = 0.002) than those in blood donors (n = 406) from a nonexposed county. No differences in IgM levels among the three groups were found after adjustment for gender and age. Home addresses of the seroresponders in the exposed county clustered to the city of the outbreak, in contrast to the scattering of addresses of the seroresponding donors in the nonexposed county. Factory employees who operated at an open biological treatment plant had significantly higher IgG and IgM levels (P < or = 0.034) than those working >200 m away. Most of the healthy seroresponders among the factory employees worked near this exposure source. Immunoblotting showed that IgG and IgM antibodies in 82.1% of all seroresponders were directed to the lipopolysaccharide of the L. pneumophila serogroup 1 outbreak strain. In conclusion, 1 year after the long-distance industrial outbreak a small increase in IgG levels of the exposed population was observed. The open biological treatment plant within the industrial premises, however, constituted a short-distance exposure source of L. pneumophila for factory employees working nearby.

Clinical isolates of Staphylococcus aureus from the Arkhangelsk region, Russia: antimicrobial susceptibility, molecular epidemiology, and distribution of Panton-Valentine leukocidin genes.

A total of 91 consecutive clinical isolates of Staphylococcus aureus were collected at the Regional Hospital of Arkhangelsk, Russia, from May to December 2004, and examined for antimicrobial susceptibility, methicillin resistance and presence of Panton-Valentine leucocidin (PVL) genes. Epidemiological typing was performed by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Methicillin-resistant S. aureus (MRSA) isolates were examined by staphylococcal cassette chromosome mec (SCCmec) typing. High-to-moderate rates of resistance to penicillin (beta-lactamase production; 93%), tetracycline (40%), erythromycin and clindamycin (32%) were observed. Forty out of ninety-one (44%) isolates were positive for PVL genes. Thirty-six (40%) PVL-positive methicillin-susceptible S. aureus (MSSA) strains were shown by PFGE and MLST typing (ST121, ST681, ST837) to be part of a nosocomial outbreak caused by clonal complex (CC) 121. PFGE, MLST and SCCmec typing revealed three MRSA clones. Sequence type (ST) 239-III (n=11), ST1097-III (n=1) and ST8-IV (n=3) belong to CC8 of epidemic multiresistant MRSA, whereas ST426-MRSA-IV/CC395 (n=1) has not been reported previously. All MRSA strains were PVL negative. The overall results underline the necessity of microbiological sampling, antimicrobial susceptibility testing, and epidemiological typing as a rational basis for antimicrobial treatment of S. aureus infections, and infection control measures to limit the spread of multiresistant MRSA and epidemic MSSA clones.

Conventional and molecular investigation of meningococcal isolates in relation to two outbreaks in the area of Athens, Greece.

Two local outbreaks caused by serogroup B Neisseria meningitidis occurred in the Athens area of Greece during 2003. In total, 30 N. meningitidis isolates from patients and carriers, as well as sporadic cases, were investigated by conventional techniques (serogroup, serotype and serosubtype), multilocus sequence typing (MLST), analysis of variable number tandem repeats (VNTR) and random amplified polymorphic DNA (RAPD) analysis. Compared with the two other molecular techniques, VNTR analysis was a simple, reliable and highly discriminatory method for fine typing of meningococcal isolates, showing a good correlation with the epidemiological data for the two outbreaks analysed.

Carriage of Streptococcus pneumoniae in healthy Norwegian children attending day-care centres.

An observational study to examine Streptococcus pneumoniae carriage in Norwegian children was initiated after two cases of pneumococcal meningitis, caused by the England(14)-9 clone, occurred in one day-care centre in Oslo. All children recruited from the day-care centre where the cases occurred were vaccinated with a seven-valent pneumococcal conjugate vaccine; the other participants who attended three other day-care centres nearby were not. The children were followed for 9 months, and three samplings took place. At the first visit, 45.7% of the children were colonised by pneumococci in the nasopharynx. The children harboured a variety of serotypes, with serotypes 6A, 23F, 6B and 19F being the most frequent. The numbers of children carrying vaccine serotypes decreased in both the vaccinated and the non-vaccinated groups. Thus, no significant effect of vaccine on carriage was detected in this relatively small study.

High case-fatality rates of meningococcal disease in Western Norway caused by serogroup C strains belonging to both sequence type (ST)-32 and ST-11 complexes, 1985-2002.

A total of 293 meningococcal disease (McD) patients from Western Norway hospitalized during 1985-2002 were examined for risk factors related to death. The case-fatality rate (CFR) increased from 4% during 1985-1993 to 17% during 1994-2002. We analysed the phenotypic and genotypic characteristics of the meningococcal patient isolates, with the aim of identifying whether highly virulent meningococcal strains contributed to the increased CFR. The Norwegian epidemic strain B:15:P1.7,16/ST-32 complex was overall the most common phenotype/genotype (n=75) and caused most deaths (n=9; CFR 12.0%). However, fatality was significantly associated with disease caused by serogroup C meningococcal strains; C:15:P1.7,16/ST-32 and C:2a/ST-11 complex strains, which had the highest CFRs of 21.1% and 18.2% respectively. Serogroup B strains of the ST-32 complex differing by serotype and/or serosubtype from the epidemic strain had a CFR of 5.1%, while the CFR of disease caused by other strains (all phenotypes and genotypes pooled) was 2.2%. The distribution of phenotypes/clonal complexes varied significantly between 1985-1993 and 1994-2002 (P<0.001); B:15/ST-32 complex strains decreased whereas both C:15:P1.7,16/ST-32 complex strains and strains with other phenotypes/clonal complexes increased. Our results indicate that C:15:P1.7,16/ST-32 and C:2a/ST-11 complex strains were highly virulent strains and contributed to the high CFR of McD in patients from Western Norway. To reduce fatality, rapid identification of such virulent strains is necessary. In addition, early and specific measures should include public information, vaccination of populations at risk of disease and carriage eradication, when clustering of patients occurs.

Macrolide-resistant Streptococcus pyogenes in Norway: population structure and resistance determinants.

A 2.7% prevalence of macrolide resistance in 1,657 Norwegian clinical Streptococcus pyogenes isolates was primarily due to erm(TR) (59%) and mef(A) (20%). Four clonal complexes comprised 75% of the strains. Macrolide resistance in S. pyogenes in Norway is imported as resistant strains or locally selected in internationally disseminated susceptible clones.

Genetic variation among Staphylococcus aureus strains from Norwegian bulk milk.

Strains of Staphylococcus aureus obtained from bovine (n = 117) and caprine (n = 114) bulk milk were characterized and compared with S. aureus strains from raw-milk products (n = 27), bovine mastitis specimens (n = 9), and human blood cultures (n = 39). All isolates were typed by pulsed-field gel electrophoresis (PFGE). In addition, subsets of isolates were characterized using multilocus sequence typing (MLST), multiplex PCR (m-PCR) for genes encoding nine of the staphylococcal enterotoxins (SE), and the cloverleaf method for penicillin resistance. A variety of genotypes were observed, and greater genetic diversity was found among bovine than caprine bulk milk isolates. Certain genotypes, with a wide geographic distribution, were common to bovine and caprine bulk milk and may represent ruminant-specialized S. aureus. Isolates with genotypes indistinguishable from those of strains from ruminant mastitis were frequently found in bulk milk, and strains with genotypes indistinguishable from those from bulk milk were observed in raw-milk products. This indicates that S. aureus from infected udders may contaminate bulk milk and, subsequently, raw-milk products. Human blood culture isolates were diverse and differed from isolates from other sources. Genotyping by PFGE, MLST, and m-PCR for SE genes largely corresponded. In general, isolates with indistinguishable PFGE banding patterns had the same SE gene profile and isolates with identical SE gene profiles were placed together in PFGE clusters. Phylogenetic analyses agreed with the division of MLST sequence types into clonal complexes, and isolates within the same clonal complex had the same SE gene profile. Furthermore, isolates within PFGE clusters generally belonged to the same clonal complex.

Molecular epidemiology of macrolide-resistant isolates of Streptococcus pneumoniae collected from blood and respiratory specimens in Norway.

Norway has a low prevalence of antimicrobial resistance, including macrolide-resistant Streptococcus pneumoniae (MRSP). In a nationwide surveillance program, a total of 2,200 S. pneumoniae isolates were collected from blood cultures and respiratory tract specimens. Macrolide resistance was detected in 2.7%. M-type macrolide resistance was found in 60% of resistant isolates, and these were mainly mef(A)-positive, serotype-14 invasive isolates. The erm(B)-encoded macrolide-lincosamide-streptogramin B (MLS(B)) type dominated among the noninvasive isolates. One strain had an A2058G mutation in the 23S rRNA gene. Coresistance to other antibiotics was seen in 96% of the MLS(B)-type isolates, whereas 92% of the M-type isolates were susceptible to other commonly used antimicrobial agents. Serotypes 14, 6B, and 19F accounted for 84% of the macrolide-resistant isolates, with serotype 14 alone accounting for 67% of the invasive isolates. A total of 29 different sequence types (STs) were detected by multilocus sequence typing. Twelve STs were previously reported international resistant clones, and 75% of the macrolide-resistant isolates had STs identical or closely related to these clones. Eleven isolates displayed 10 novel STs, and 7/11 of these "Norwegian strains" coexpressed MLS(B) and tetracycline resistance, indicating the presence of Tn1545. The invasive serotype-14 isolates were all classified as ST9 or single-locus variants of this clone. ST9 is a mef-positive M-type clone, commonly known as England(14)-9, reported from several European countries. These observations suggest that the import of major international MRSP clones and the local spread of Tn1545 are the major mechanisms involved in the evolution and dissemination of MRSP in Norway.