P. A. C. Maple

WORLD-WIDE ANTIBIOTIC RESISTANCE IN METHICILLIN-RESISTANT STAPHYLOCOCCUS AUREUS

Antibiotic resistance patterns were determined for 106 strains of methicillin-resistant Staphylococcus aureus (MRSA) from 21 countries. Resistance to gentamicin, tobramycin, netilmicin, amikacin, streptomycin, or erthromycin was recorded in more than 90% of strains. Resistance to the other compounds tested was as follows: tetracycline 86%, minocycline 76%, trimethoprim 69%, clindamycin 66%, neomycin 59%, chloramphenicol 39%, rifampicin 26%, fosfomycin 22%, ciprofloxacin 17%, fusidic acid 12%, bacitracin 2%, and novobiocin 1%. All the stains were sensitive to mupirocin, pristinamycin, ramoplanin, teicoplanin, and vancomycin. There were geographical patterns of resistance: MRSA from the UK and Australia were predominantly resistant to trimethoprim, whereas many strains from centres in Europe and the USA were sensitive. MRSA that were resistant to ciprofloxacin were of French and German origin. 15 strains, 12 of which came from France, Turkey, or Brazil, were resistant either to thirteen or to fourteen agents.

The seroepidemiology of Bordetella pertussis infection in Western Europe

High titres of pertussis toxin (PT) antibody have been shown to be predictive of recent infection with Bordetella pertussis. The seroprevalence of standardized anti-PT antibody was determined in six Western European countries between 1994 and 1998 and related to historical surveillance and vaccine programme data. Standardized anti-PT titres were calculated for a series of whole-cell and acellular pertussis vaccine trials. For the serological surveys, high-titre sera (> 125 units/ml) were distributed throughout all age groups in both high- (> 90%) and low-coverage (< 90%) countries. High-titre sera were more likely in infants in countries using high-titre-producing vaccines in their primary programme (Italy, 11.5%; Western Germany, 13.3%; France, 4.3%; Eastern Germany, 4.0%) compared to other countries (The Netherlands, 0.5%; Finland, 0%). Recent infection was significantly more likely in adolescents (10-19 years old) and adults in high-coverage countries (Finland, The Netherlands, France, East Germany), whereas infection was more likely in children (3-9 years old) than adolescents in low-coverage (< 90%; Italy, West Germany, United Kingdom) countries. The impact and role of programmatic changes introduced after these surveys aimed at protecting infants from severe disease by accelerating the primary schedule or vaccinating older children and adolescents with booster doses can be evaluated with this approach.

The sero-epidemiology of diphtheria in Western Europe

Seven countries in Western Europe collected large, representative serum banks across the entire age range and tested them for diphtheria anti-toxin (sample size ranged from 2991 to 7715). Although a variety of assays were used, the results were all standardized to those of a reference laboratory and expressed in international units. The standardization process, and the availability of similar, large data sets allowed comparative analyses to be performed in which a high degree of confidence could be ascribed to observed epidemiological differences. The results showed that there were large differences in the proportion of adults with insufficient levels of protection amongst different countries. For instance, roughly 35% of 50- to 60-year-olds were found to be seronegative (titre < or = 0.01 IU/ml) in Finland compared with 70-75% in the United Kingdom. Furthermore, the proportion of seronegative adults would be expected to increase in some countries, notably Italy and the western part of Germany. In those countries with vaccination of military recruits there was a marked sex-related difference in the proportion of seropositive individuals. All countries have high levels of infant vaccine coverage (> 90%) but the accelerated schedule in the United Kingdom appears to result in lower anti-toxin titres than elsewhere. In Sweden, booster doses are not offered until 10 years of age which results in large numbers of children with inadequate levels of protection. Although the United Kingdom and Sweden both have higher proportions of seronegative children than elsewhere the likelihood of a resurgence of diphtheria in these countries seems remote.

Diphtheria immunity in UK blood donors

Immunity to diphtheria was determined in serum samples from 1000 UK-born blood donors at the North London Blood Transfusion Centre during a three-month period in 1993; 125 women and 125 men were stratified in 10-year age groups, from 20 to 59. A tissue (vero cell)-culture toxin-neutralisation assay was used to measure serum diphtheria antitoxin concentrations. According to internationally accepted definitions (antitoxin < 0.01 IU/mL = susceptibility, 0.01-0.09 IU/mL = basic protection, and > or = 0.1 IU/mL = full protection), 37.6% of donors were susceptible to diphtheria, 31.5% had basic protection, and 30.9% were fully protected. Log-linear modelling of the influence of age and sex on population immunity showed a significant trend (p < 0.001) of decreasing immunity with increasing age: 25.2% of donors aged 20-29 were susceptible compared with 52.8% of those aged 50-59. There was a small sex effect (p = 0.052); similar proportions of men and women were susceptible, but fewer women had full protection. There was no age-sex interaction on immunity (p = 0.454). Our results suggest that booster immunisation of adults is necessary to increase herd immunity of the adult population.

European Sero-Epidemiology Network: standardisation of the assay results for pertussis

A standardisation process was developed in order to compare and harmonize serological results of pertussis toxin (PT) antibody measurements performed by laboratories using different technical procedures for detection. This involved the development of a common panel, of sera by a designed reference centre, the distribution of the panel to each participating laboratory for testing with their routine methods, the comparison of the obtained results to those of the reference centre, and the calculation of standardisation equations by regressing the quantitative results against those of the reference centre. As a cut-off indicative of protection against pertussis has not yet been defined, a particular emphasis was laid upon achieving standardisation of high titre results that would allow epidemiological evaluations based on the estimation of the incidence of recent infections rather than on the traditional approach of determining the population immunity profile. A generally good agreement was achieved between the participating laboratories, all using ELISA procedures very similar in many crucial aspects, and standardisation equations were produced useful to enable inter-country comparison during the next stages of the European Sero-Epidemiology Network (ESEN) project concerning the serological surveillance of immunity to pertussis in Europe.

European sero-epidemiology network: standardisation of the results of diphtheria antitoxin assays.

A European Sero-Epidemiological Network (ESEN) was established with the aim to co-ordinate and harmonise serological surveillance of immunity to communicable diseases in Europe. In this study the inter-laboratory standardisation of diphtheria toxin antibody measurements is reported. A standard panel of 162 sera was tested by the participating laboratories using an in vitro assay of their choice: VERO cell toxin neutralisation assay (NT), double-antigen delayed time-resolved fluorescence immuno-assay (DA-DELFIA), double-antigen enzyme-linked immunosorbent assay (DAE), toxin binding inhibition test (ToBI) and an indirect enzyme-linked immunosorbent assay (ELISA). The results were standardised using regression against the NT. The variations due to inter-laboratory and inter-assay variation, which would otherwise make it difficult directly to compare the main serum bank results by the different laboratories and the various assays were successfully minimised by the standardisation. The regression equations obtained will be used to transform the respective local results of testing the main serum bank into the reference test unitages. This study also gave the opportunity to compare the various assays within and between laboratories. This demonstrated a very high correlation between DA-DELFIA, DAE, ToBI and the NT. The ELISA showed a good correlation, too, however sera below some 0.1 IU/ml were overestimated.

Performance of a Time-Resolved Fluorescence Immunoassay for Measuring Varicella-Zoster Virus Immunoglobulin G Levels in Adults and Comparison with Commercial Enzyme Immunoassays and Merck Glycoprotein Enzyme Immunoassay

ABSTRACT Highly sensitive and specific, quantitative assays are needed to detect varicella-zoster virus (VZV) immunoglobulin G in human sera, particularly for determining immune status and response following vaccination. A time-resolved fluorescence immunoassay (TRFIA) has been developed, and its performance was compared to that of two commercial enzyme immunoassays (EIAs) and Merck glycoprotein EIA (gpEIA). The TRFIA had equivalent sensitivity (97.8%) and high specificity (93.5%) in relation to gpEIA. A commercial (Behring) EIA compared favorably with TRFIA in terms of sensitivity (98.4%) but had lower specificity (80.7%). Another commercial EIA (Diamedix) had high specificity (97.1%) but low sensitivity (76.4%) compared to TRFIA if equivocal test results were treated as negative for VZV antibody. A novel feature of the TRFIA was that the cutoff was generated using population mixture modeling and was expressed in mIU/ml, as the assay was calibrated using the British standard VZV antibody.

Prevalence of Anti-Varicella-Zoster Virus Antibodies in French Infants under 15 Months of Age

ABSTRACT Varicella is a widespread disease of childhood resulting from primary infection with varicella-zoster virus (VZV). The objective of this study was to determine the kinetics of the decline of maternal anti-VZV antibodies in French infants between birth and the age of 15 months in order to estimate the duration of passively acquired maternal anti-VZV immunoglobulin G (IgG). This prospective multicenter study was conducted between October 2005 and January 2007 in the pediatric wards and/or pediatric emergency units of seven French hospitals scattered throughout the country. The level of anti-VZV IgG antibodies in serum was measured by a time-resolved fluorescence immunoassay (TRFIA) (the threshold considered positive is 150 mIU/ml). A total of 345 infants were included. Seventy-seven percent of mothers reported a history of varicella. A rapid decline in the prevalence of anti-VZV antibodies was observed during the first few months of life, with the mean antibody titer decreasing from 536 mIU/ml at birth and through 1 month to below the 150-mIU/ml threshold at 3 to 4 months. The half-life of passively acquired maternal immunoglobulins was around 6 weeks. Based on a large number of subjects, this study clearly demonstrated, for the first time in France, high levels of passively acquired maternal antibodies during the neonatal period, and it allowed us to estimate the duration of passively acquired maternal anti-VZV IgG in French infants. After 4 to 5 months, infants had very low levels of maternal anti-VZV IgG, below the 150-mIU/ml cutoff of the VZV IgG TRFIA.

Characterization of Treponema pallidum Particle Agglutination Assay-Negative Sera following Screening by Treponemal Total Antibody Enzyme Immunoassays

ABSTRACT Following a laboratory audit, a significant number of Treponema pallidum particle agglutination assay (TPPA)-negative sera were identified when TPPA was used as a confirmatory assay of syphilis enzyme immunoassay (EIA) screening-reactive sera (SSRS). Sera giving such discrepant results were further characterized to assess their significance. A panel of 226 sera was tested by the Abbott Murex ICE Syphilis EIA and then by the Newmarket Syphilis EIA II. TPPA testing was performed on 223 sera. Further testing by the Venereal Disease Research Laboratory (VDRL) test, the Mercia Syphilis IgM EIA, the fluorescent treponemal antibody (FTA-ABS) assay, and INNO-LIA immunoblotting was undertaken in discrepant cases. One hundred eighty-seven of 223 (83.8%) SSRS were TPPA reactive, while 26 (11.6%) sera which were reactive in both the ICE and Newmarket EIAs were nonreactive by TPPA. The majority (68%) of the TPPA-discrepant sera were from HIV-positive patients and did not represent early acute cases, based on previous or follow-up samples, which were available for 22/26 samples. FTA-ABS testing was performed on 24 of these sera; 14 (58.3%) were FTA-ABS positive, and 10 (41.7%) were FTA-ABS negative. Twenty-one of these 26 sera were tested by INNO-LIA, and an additional 4 FTA-ABS-negative samples were positive. In this study, significant numbers (18/26) of SSRS- and TPPA-negative sera were shown by further FTA-ABS and LIA (line immunoblot assay) testing to be positive. The reason why certain sera are negative by TPPA but reactive by treponemal EIA and other syphilis confirmatory assays is not clear, and these initial findings should be further explored.

Differing activities of quinolones against ciprofloxacin-susceptible and ciprofloxacin-resistant, methicillin-resistant Staphylococcus aureus.

The in vitro activities of nine quinolones (seven fluoroquinolones, nalidixic acid, and acrosoxacin) against methicillin-resistant Staphylococcus aureus (MRSA) were compared with those of the glycopeptides teicoplanin and vancomycin. MICs against 160 strains of ciprofloxacin-susceptible (MIC, less than 2.0 micrograms/ml) MRSA and 40 strains of ciprofloxacin-resistant (MIC, greater than or equal to 2.0 micrograms/ml) MRSA were determined. The following MICs for 50% of the strains tested (in micrograms per milliliter) were obtained for ciprofloxacin-susceptible and -resistant strains, respectively: tosufloxacin, 0.06 and 2.0; ofloxacin, 0.25 and 16; ciprofloxacin, 0.5 and 16; pefloxacin, 0.5 and 32; acrosoxacin, 1.0 and greater than 256; enoxacin, 1.0 and 64; fleroxacin, 1.0 and 32; norfloxacin, 2.0 and 64; nalidixic acid, 64 and 512; teicoplanin, 1.0 and 1.0; vancomycin, 2.0 and 2.0. In mutation rate studies using a range of antibiotic concentrations to reflect those achievable in vivo, resistant mutants grew only on plates containing nalidixic acid (rate of mutation to resistance, 10(-7) to 10(-8) and on plates containing low concentrations of ciprofloxacin, enoxacin, and norfloxacin (rate of mutation to resistance, 10(-8) to 10(-9). In time-kill studies, 99.9% killing was found within 8 h for all of the quinolones tested (norfloxacin and nalidixic acid were not tested). Teicoplanin and vancomycin were less rapidly bactericidal. For the clinical isolates of ciprofloxacin-resistant MRSA, different levels and patterns of quinolone resistance were found. Generally, cross-resistance among the fluoroquinolones was complete; however, incomplete cross-resistance did occur with the nonfluorinated quinolone acrosoxacin.