Analysis of Bordetella pertussis clinical isolates circulating in European countries during the period 1998-2012.

Despite more than 50 years of vaccination, pertussis is still an endemic disease, with regular epidemic outbreaks. With the exception of Poland, European countries have replaced whole-cell vaccines (WCVs) by acellular vaccines (ACVs) in the 1990s. Worldwide, antigenic divergence in vaccine antigens has been found between vaccine strains and circulating strains. In this work, 466 Bordetella pertussis isolates collected in the period 1998-2012 from 13 European countries were characterised by multi-locus antigen sequence typing (MAST) of the pertussis toxin promoter (ptxP) and of the genes coding for proteins used in the ACVs: pertussis toxin (Ptx), pertactin (Prn), type 2 fimbriae (Fim2) and type 3 fimbriae (Fim3). Isolates were further characterised by fimbrial serotyping, multi-locus variable-number tandem repeat analysis (MLVA) and pulsed-field gel electrophoresis (PFGE). The results showed a very similar B. pertussis population for 12 countries using ACVs, while Poland, which uses a WCV, was quite distinct, suggesting that ACVs and WCVs select for different B. pertussis populations. This study forms a baseline for future studies on the effect of vaccination programmes on B. pertussis populations.

Investigations into the emergence of pertactin-deficient Bordetella pertussis isolates in six European countries, 1996 to 2012.

Pathogen adaptation has been proposed to contribute to the resurgence of pertussis. A striking recent example is the emergence of isolates deficient in the vaccine component pertactin (Prn). This study explores the emergence of such Prn-deficient isolates in six European countries. During 2007 to 2009, 0/83 isolates from the Netherlands, 0/18 from the United Kingdom, 0/17 Finland, 0/23 Denmark, 4/99 Sweden and 5/20 from Norway of the isolates collected were Prn-deficient. In the Netherlands and Sweden, respectively 4/146 and 1/8 were observed in a later period (2010­12). The Prn-deficient isolates were genetically diverse and different mutations were found to inactivate the prn gene. These are indications that Prn-deficiency is subject to positive selective pressure. We hypothesise that the switch from whole cell to acellular pertussis vaccines has affected the balance between 'costs and benefits' of Prn production by Bordetella pertussis to the extent that isolates that do not produce Prn are able to expand. The absence of Prn-deficient isolates in some countries may point to ways to prevent or delay the spread of Prn-deficient strains. In order to substantiate this hypothesis, trends in the European B. pertussis population should be monitored continuously.

Seroepidemiology of pertussis in a cross-sectional study of an adult general population in Denmark.

An increase in pertussis has been observed in several countries over the last decades, especially in adult populations. The seroprevalence of pertussis was determined in a cross-sectional study of the adult population in the Copenhagen area, Denmark, conducted between 2006 and 2008. Specific IgG antibodies against pertussis toxin (PT) were measured in 3440 persons resulting in an age-standardized seroprevalence of 3.0% (95% confidence interval 1.9-4.7) using an IgG anti-PT cut-off of 75 IU/ml. By using antibody decay profiles from longitudinal data the estimated seroincidence was 143/1000 person-years. In contrast, an incidence of 0.03/1000 person-years was estimated from the official data of notified cases during the same period. Of the investigated risk factors, only age and education were significantly associated with pertussis infection. This study indicates that pertussis is highly underestimated in the adult population in Denmark, which has implications for future prevention strategies, including raising the awareness of pertussis.

Evaluation of PCR methods for the diagnosis of pertussis by the European surveillance network for vaccine-preventable diseases (EUVAC.NET).

This study aimed to evaluate the performance of polymerase chain reaction (PCR) methods used for the diagnosis of pertussis in laboratories within Europe in 2011. National reference laboratories in 25 European countries were contacted and a total of 24 laboratories from 19 countries agreed to participate in the study. A panel of seven samples of DNA from Bordetella pertussis, Bordetella parapertussis and Bordetella holmesii plus a negative control were distributed and analysed according to the routine PCR methods in each laboratory. The study took place in 2011. Nineteen laboratories used a real-time PCR approach, four laboratories used block-based PCR and one laboratory used a combination of methods. Six different combinations of amplification targets were used, and ten laboratories tested only for the presence of B. pertussis DNA. All laboratories (24/24) correctly identified a sample with high concentration of B. pertussis DNA, while three misidentified the B. parapertussis DNA as B. pertussis and 15 misidentified the B. holmesii DNA as either B. pertussis or B. parapertussis. There was a wide variation in the methods used for PCR-based diagnosis of pertussis among the European laboratories. Several laboratories were not able to discriminate between DNA samples from different Bordetella species.

Detecting non-typhoid Salmonella in humans by ELISAs: a literature review.

Non-typhoid salmonellosis is one of the most common causes of foodborne illness throughout the world. Serological methods for the diagnosis of Salmonella infections vary widely and the most commonly used test is limited by high running costs as well as low sensitivity and specificity. Fast and reliable immunoassays which detect subunit antigens for Salmonella enterica subsp. enterica serovar Typhi are commercially available but at present there is no international consensus on similar tests for non-typhoid salmonellosis. In contrast to the veterinary and food sectors, most immunoassays for non-typhoid human Salmonella diagnosis are developed in-house and used in-house for research or surveillance purposes, rather than for routine diagnostics. Considering the current burden of disease, the development of a validated and standardized, commercially available antibody assay for diagnosing non-typhoid human salmonellosis could be of great benefit for diagnostic and surveillance purposes throughout the world.

Validation of an ELISA for the diagnosis of recent Campylobacter infections in Guillain-Barré and reactive arthritis patients.

Weeks or months following Campylobacter infection, a small proportion of infected individuals develop Guillain-Barré syndrome (GBS) or reactive arthritis (ReA). Stool culture for Campylobacter is often negative in these patients, and serology is therefore the method of choice for diagnosing a recent infection with Campylobacter. This study developed a capture ELISA system to detect anti-Campylobacter IgA and IgM antibodies indicative of a recent infection. The sensitivity of the assay was 82.0% in uncomplicated Campylobacter enteritis patients, 96.2% in GBS patients who were culture-positive for Campylobacter, and 93.1% in culture-positive ReA patients, with a specificity of 93.0%. The assay allows identification of Campylobacter infection in patients with post-infectious neurological and rheumatological complications.

Rosenbluth chain cluster growth in the study of micelle self-assembly.

A Rosenbluth algorithm [J. Chem. Phys. 23, 356 (1955)] for enumerating clusters of chains is presented. The method is used to undertake a direct enumeration of the cluster partition function for small clusters in a three-dimensional lattice model of a binary mixture of amphiphile and solvent. In this model, the amphiphiles are represented as connected chains on a lattice, with vacant sites representing the solvent. The results from the Rosenbluth method are compared with those obtained by Metropolis Monte Carlo simulations which allow free self-assembly of clusters. The agreement between the two methods allows an unambiguous identification of the packing entropy associated with micelle self-assembly. Results are presented for unbranched chains having two head and four tail segments (H2T4) and also four head and four tail segments (H4T4). Although the cluster enumeration method described in this paper has been developed for micellar systems, it will have applications in a variety of areas including nucleation and percolation.

The relation of lightness and stereoscopic depth in a simple viewing situation.

The effect of stereoscopic depth on perceived lightness was studied using a simple, achromatic stimulus arrangement. In Experiment 1, depth/lightness interactions were sought between a single test field and a single induction field. In Experiment 2, depth/lightness interactions were looked for between a single test field and two induction fields. Stimuli were presented on a computer screen and viewed with a stereoscope. The subjects reported perceived lightness of the achromatic test field by rating its apparent blackness along a dimension of 0%-100%. In Experiment 1, they reported lightness judgments of the test field across 13 perceived depth levels and 8 contrast levels. In Experiment 2, they gave lightness judgments of the test field across 7 perceived depth levels and 16 contrast levels. We were particularly interested in observing the generality of Gilchrist's coplanar ratio hypothesis. The results showed that when stereopsis and contrast levels are the available cues, depth and lightness percepts are independent, and it is retinal ratios, not coplanar ratios, that dictate lightness perception. We conclude that before the relative depth location of an object is determined, its lightness value is known through sensory-level processes.