BACKGROUND: In December 2004, a 3-dose (2, 4, & 12 months) PCV7 program was implemented for routine immunization of infants along with "passive" catch-up vaccination for children aged up to 4 years.Uptake was high and 90% of children aged 2 months at the launch of the program had received = 3 doses by age 2 years.PURPOSE: To analyse age-specific trends in IPD incidence and serotype distribution.METHODOLOGY: IPD cases were extracted from the provincial registry of notifiable disease which is essentially based on reports from public hospital laboratories and the provincial reference laboratory.RESULTS: Overall IPD incidence decreased from 10.9/100,000 personyears in 1999-2001 (before PCV was licensed in Canada) to a minimum of 8.6/100,000 in 2006, and increased to 9.8/100,000 in 2007.The same pattern was observed in all age groups.The initial decrease was associated with a diminishing occurrence of PCV7 serotypes and was most marked in children aged less than 2 years.In this age group, the incidence of PCV7 serotypes (adjusted for incomplete serotype identification) decreased from 87.3/100,000 in 1999-2001, to 4.4/100,000 in 2007 (95% reduction).The secondary increase was caused by PCV-related serotypes (mainly 19A), and non-PCV7 serotypes (mainly 12F, 33A and 7F), and was also more marked in children aged less than 2 years than in older age groups.CONCLUSION: Direct vaccine protection in conjunction with herd immunity are competing with clonal evolution and ecological replacement involving Sp serotypes not included in or imperfectly covered by PCV7.Nobody knows where and when equilibrium between these two antagonist forces will be reached.
ABSTRACT In a context of worldwide emergence of resistance among Streptococcus pneumoniae strains, early detection of strains with decreased susceptibility to β-lactam antibiotics is important for clinicians. If the 1-μg oxacillin disk diffusion test is used as described by the National Committee for Clinical Laboratory Standards, no interpretation is available for strains showing zone sizes of ≤19 mm, and there is presently no disk diffusion test available for screening cephalosporin resistance. The zones obtained by the diffusion method by using the 1-μg oxacillin disk were compared with penicillin MICs for 1,116 clinical strains and with ceftriaxone MICs for 695 of these strains. Among the 342 strains with growth up to the 1-μg oxacillin disk margin, none were susceptible (MIC, ≤0.06 μg/ml), 62 had intermediate resistance (MIC, 0.12 to 1.0 μg/ml), and 280 were resistant (MIC, ≥2.0 μg/ml) to penicillin. For ceftriaxone, among 98 strains with no zone of inhibition in response to oxacillin, 68 had intermediate resistance (MIC, 1.0 μg/ml), and 22 were resistant (MIC, ≥2.0 μg/ml). To optimize the use of the disk diffusion method, we propose that the absence of a zone of inhibition around the 1-μg oxacillin disk be regarded as an indicator of nonsusceptibility to penicillin and ceftriaxone and recommend that such strains be reported as nonsusceptible to these antimicrobial agents, pending the results of a MIC quantitation method.
OBJECTIVE: To determine the susceptibility of group A beta‐hemolytic streptococci (GABHS) in the lower St Lawrence region, Quebec to different antibiotics, particularly macrolides, and to compare different antibiogram methods (disk diffusion, E‐test and microdilution) and incubation atmospheres (ambient air and 5% carbon dioxide). METHODS: A total of 384 strains of GABHS isolated from 377 patients (throat 335; other sites 49) from three hospitals in the lower St Lawrence region were analyzed for their susceptibility to erythromycin, clarithromycin, azithromycin, penicillin, clindamycin, cephalothin, rifampin and vancomycin by disk diffusion on Mueller‐Hinton (MH) agar supplemented with 5% defibrinated sheep blood (MHB) at 35ºC in 5% carbon dioxide. Strains that were found to be intermediately resistant or resistant to one of the antibiotics by disc diffusion, strains from sites other than throat, and a sample of 97 pharyngeal strains were evaluated by E‐test on MHB (35ºC, 5% carbon dioxide) for their susceptibility to the antibiotics erythromycin, clarithromycin, azithromycin, penicillin, clindamycin and ceftriaxone. In addition, minimum inhibitory concentrations (MICs) were determined for erythromycin and azithromycin by broth microdilution using MH broth supplemented with 2.5 % of lysed horse blood (35ºC, ambient air) on strains that were resistant or intermediately resistant to the macrolides (erythromycin, clarithromycin, azithromycin). An evaluation was also carried out on these strains to determine the influence of the incubating atmosphere (ambient air versus 5% carbon dioxide) on susceptibility results obtained by disk diffusion (erythromycin, clarithromycin and azithromycin) and E‐test (erythromycin and azithromycin) methods. RESULTS: Nine strains (2%) from nine patients (throat eight, pus one) were resistant to all macrolides as tested by three different techniques (disk diffusion, E‐test and microdilution). All strains were susceptible to all the other antibiotics tested. For the strains intermediately resistant or resistant to macrolides, incubation in a 5% carbon dioxide atmosphere was associated with a reduction in the diameter of inhibition determined by disk diffusion (P<0.001) with frequent minor variations in interpretation, and with an increase in the MIC by E‐test (P<0.001), which had no impact on interpretation. CONCLUSIONS: Resistance of GABHS to macrolides was not common (2%) in the lower St Lawrence Region. GABHS susceptibility to erythromycin seemed to predict the susceptibility to the other macrolides. Significant variation in antibiogram results (disk diffusion and E‐test) of GABHS susceptibility to macrolides was related to the incubation atmosphere and may have an impact on the interpretation of disk diffusion results.
A stem-loop termed the kissing-loop hairpin is one of the most highly conserved structures within the leader of human immunodeficiency virus type 1 (HIV-1) and chimpanzee immunodeficiency virus genomic RNA. Because it plays a key role in the in vitro dimerization of short HIV-1 RNA transcripts (M. Laughrea and L. Jette, Biochemistry 35:1589-1598, 1996, and references therein; M. Laughrea and L. Jette, Biochemistry 35:9366-9374, 1996, and references therein) and because dimeric RNAs may be preferably encapsidated into the HIV-1 virus, alterations of the kissing-loop hairpin might affect the in vivo dimerization and encapsidation processes. Accordingly, substitution and deletion mutations were introduced into the kissing-loop hairpin of an infectious HIV-1 molecular clone in order to produce viruses by transfection methods. The infectivity of the resulting viruses was decreased by at least 99%, the amount of genomic RNA packaged per virus was decreased by 50 to 75%, and the proportion of dimeric genomic RNA was reduced from >80 to 40 to 50%, but the dissociation temperature of the genomic RNA was unchanged. There is evidence suggesting that the deletion mutations moderately inhibited CAp24 production but had no significant effect on RNA splicing. These results are consistent with the kissing-loop model of HIV-1 RNA dimerization. In fact, because intracellular viral RNAs are probably more concentrated in transfected cells than in cells infected by one virus and because the dimerization and encapsidation processes are concentration dependent, it is likely that much larger dimerization and encapsidation defects would have been manifested within cells infected by no more than one virus.
Phage typing of 13,579 clinical and environmental strains of Staphylococcus aureus received at the Quebec Public Health Laboratory between 1976 and 1983 was routinely performed to assess the distribution of lytic groups. Strains susceptible to phages 94, 95, and 96 predominated and accounted for 25% of the specimens. The distribution of strains in lytic groups varied with time and specimen source.
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