N. Orr

Double-blind vaccine-controlled randomised efficacy trial of an investigational Shigella sonnei conjugate vaccine in young adults

BACKGROUND The aim of this double-blind randomised vaccine-controlled trial was to assess the efficacy of a conjugate vaccine composed of Shigella sonnei O-specific polysaccharide bound to Pseudomonas aeruginosa recombinant exoprotein A (S sonnei-rEPA) and of an oral, live-attenuated Escherichia coli/S flexneri 2a (EcSf2a-2) hybrid vaccine among military recruits in Israel at high risk of exposure to Shigella spp. We report here our preliminary findings on the efficacy of S sonnei-rEPA; we have not documented sufficient cases to assess the efficacy of EcSf2a-2. METHODS Between April, 1993, and August, 1994, male Israeli Military recruits aged 18-22 years were asked to take part in our study. We enrolled 1446 soldiers from seven separate field sites (groups A-G). Soldiers were randomly allocated one injection of S sonnei-rEPA and four doses of oral placebo (n = 576), four oral doses of EcSf2a-2 and one injection of saline placebo (n = 580), or one injection of meningococcal tetravalent control vaccine and four doses of oral placebo (n = 290). Because there were no cases of S flexneri 2a, the EcSf2a-2 and meningococcal vaccines were the control group. We defined S sonnei shigellosis as diarrhoea with a positive faecal culture for S sonnei. Each group of soldiers was followed up for 2.5-7.0 months. The primary endpoint was protective efficacy of S sonnei-rEPA against S sonnei shigellosis. FINDINGS Cases of culture-proven S sonnei shigellosis occurred in four groups of soldiers (groups A-D), which comprised 787 volunteers (312 received S sonnei-rEPA, 316 received EcSf2a-2, and 159 received meningococcal control vaccine). In groups A-C, cases of shigellosis occurred 70-155 days after vaccination, whereas in group D cases occurred after 1-17 days. In groups A-C, the attack rate of shigellosis was 2.2% in recipients of S sonnei-rEPA compared with 8.6% in controls (protective efficacy 74% [95% CI 28-100], p = 0.006). S sonnei-rEPA also showed significant protection against shigellosis in group D (43% [4-82], p = 0.039). Prevaccination and postvaccination ELISA measurements of antibody to S sonnei lipopolysaccharide among recipients of S sonnei-rEPA showed that the vaccinees who developed S sonnei shigellosis had significantly lower serum IgG and IgA responses to the homologous lipopolysaccharide than those who did not (p = < 0.05). INTERPRETATION One injection of S sonnei-rEPA confers type-specific protection against S sonnei shigellosis. The high antibody concentration induced by the conjugate vaccine in volunteers who did not develop shigellosis suggests that there is an association between serum antibody titre and protection.

A Cluster of Ecthyma Outbreaks Caused by a Single Clone of Invasive and Highly Infective Streptococcus pyogenes

BACKGROUND Ecthyma is an invasive, ulcerated skin infection. Four ecthyma outbreaks occurred in different infantry units in the Israeli Defense Force from October 2004 through February 2005. Morbidity attack rates in the first 3 outbreaks were 89% (49 of 55 soldiers), 73% (32 of 44), and 82% (37 of 45). In the fourth outbreak, in which early intervention (antimicrobial treatment and improvement of hygiene) was applied, the attack rate was 25% (10 of 40 soldiers). In the first outbreak cluster, 4 soldiers experienced poststreptococcal glomerulonephritis, and 5 cases of systemic sequelae were recorded (1 case of severe septic shock, 3 cases of pneumonia, and 1 case of septic olecranon bursitis). METHODS Streptococcus pyogenes and Staphylococcus aureus were isolated from ecthyma sores, oropharynx, and anterior nares of affected and unaffected soldiers involved in all 4 outbreaks. RESULTS Although the S. aureus isolates had different genomic profiles, >90% of S. pyogenes isolates were identified as belonging to a single clone, emm type 81, T type 8. Epidemiological investigation revealed that the hygiene levels of the soldiers and their living conditions were probably the most important cause for the difference in attack rates, wound severity, and systemic sequelae found between and within the units. CONCLUSIONS Our study demonstrates the possible ramifications of the combination of a virulent and highly infective S. pyogenes strain and poor living conditions, and it emphasizes the importance of early intervention in such conditions.

An outbreak of pertussis among young Israeli soldiers

In winter 2001, an outbreak of pertussis involving an estimated 75 people occurred among soldiers serving in an infantry regiment of the Israeli Defense Forces (IDF). Nasopharyngeal swabs were obtained from patients and contacts for culture and PCR. Serum samples were obtained and assayed by ELISA for the presence of IgA, IgM and IgG antibodies to a lysate antigen of Bordetella pertussis. The calculated attack rate was 21% based on clinical signs alone (cough lasting 30 days or longer) and 9.5% based on clinical signs with laboratory confirmation (by PCR, IgA or IgM). A high carriage rate was observed; 20% of the asymptomatic and previously symptomatic subjects were PCR-positive for B. pertussis. These findings emphasize the importance of B. pertussis as a causative agent of epidemic respiratory infections in young adults and reveal the occurrence of a significant proportion of pertussis transient carriers during an outbreak of the disease.

Prospective Cohort Studies of Shigellosis During Military Field Training

Abstract Epidemiological and clinical features of shigellosis occurring among cohorts of Israeli recruits followed-up for 3–6 months during the summer field training of years 1993–1997 were studied. The incidence rate of culture-proven shigellosis was the highest (78 cases per 1,000 recruits) in 1996 and the lowest (13 cases per 1,000 recruits) in 1995. Shigella sonnei (152 isolates) and Shigella flexneri (151 isolates) were the most common species. Fifty percent of the patients with shigellosis had fever (>37.5  °C), compared to only 18% of the subjects with other diarrheal diseases (P<0.001). The duration of illness was longer among subjects with shigellosis than among those with other diarrheal diseases (P<0.001). Illness due to Shigella flexneri was more severe than illness caused by Shigella sonnei.

Correlation of IgA, IgM and IgG antibody-detecting assays based on filamentous haemagglutinin, pertussis toxin and Bordetella pertussis sonicate in a strictly adult population

Pertussis diagnosis among adults is primarily based on serology. In this study, receiver operation characteristics (ROC) analysis was utilized to evaluate three IgA, IgM and IgG ELISAs based on B. pertussis whole-cell sonicate (WC), pertussis toxin (PT), or combined PT-filamentous haemagglutinin (FHA) antigens in a healthy adult population and in adults suffering from symptoms consistent with pertussis. The assays were compared to a PT and FHA reference ELISA. The reference assay showed high correlation with PT- and PT-FHA-based ELISAs but low correlation was found with the WC-based ELISA. However, ROC analysis indicated that all the assays enabled fine differentiation between healthy subjects and subjects suffering from symptoms suggestive of pertussis. The WC IgA ELISA showed the best diagnostic performance [highest specificity (98.8%) with highest sensitivity (53.8%)]. We conclude that despite a low correlation between the various assays they all carry good diagnostic capability for an adult population.

Retrospective Analysis of the First Clonal Outbreak of Nalidixic Acid-Resistant Shigella sonnei Shigellosis in Israel

Abstract Reported here is a retrospective molecular analysis of the isolates recovered from the first outbreak of nalidixic acid (NA)-resistant Shigella sonnei shigellosis to occur in Israel. The outbreak affected 94 children. In the retrospective analysis, a total of 13 NA-resistant isolates and five NA-susceptible isolates recovered during the outbreak period were examined. Restriction fragment length polymorphism profiles obtained by digestion with BamHI, PvuI, HinfI or SmaI yielded identical profiles for all 18 isolates. All NA-resistant strains had an identical plasmid profile, but this profile differed from that displayed by the susceptible strains. In all of the NA-resistant strains a 304 bp fragment in the gyrA gene coding for a region associated with NA resistance was sequenced and showed a single point mutation, Ser83→Phe. In this outbreak, the isolates of NA-resistant Shigella sonnei belonged to a single clone and NA resistance was associated with a point mutation in the gyrA gene.

Safety and immunogenicity of the oral E. coli K12-S. flexneri 2a vaccine (EcSf2a-2) among Israeli soldiers

A double-blind placebo-controlled study was carried out on the safety and immunogenicity of the oral Shigella flexneri (EcSf2a-2) vaccine among Israeli soldiers. Sixty volunteers received the vaccine and 59 received placebo. Fifty-three were given the full vaccine regimen (four doses). Doses ranged between 4.1 x 10(8) and 1.1 x 10(9) c.f.u. Visits to the unit clinic for mild gastrointestinal symptoms were common after the first dose in vaccinees (13%) as compared with placebo recipients (5%), but the difference was not significant, p = 0.12. Similarly, there was no difference between the groups for either gastrointestinal or non-gastrointestinal complaints reported by questionnaire. The vaccine strain was excreted by 69% and 67% of the vaccinees one day after receiving the second and the fourth doses, respectively. As judged by antibiotic susceptibility, phage typing and restriction fragment length polymorphism (RFLP), the vaccine strain emerged as genetically stable after replication in human gut and shedding. There was neither bacteriological nor serological evidence of transmission of the vaccine from vaccinees to placebo recipients. Eighteen of 26 (69.2%) and 11 of 30 (36.7%) vaccinees had significant IgA secreting cell responses 7 and 21 days after the first dose, respectively. Significant IgA or IgG serum antibody response to S. flexneri 2a LPS was detected in 30% of the vaccinees. These results support further evaluation of EcSf2a-2 vaccine protective efficacy in field studies.

Molecular analysis of noroviruses involved in acute gastroenteritis outbreaks in military units in Israel, 1999-2004

The study presented here was conducted to determine the genetic properties of noroviruses (NoVs) identified between 1999 and 2004 in army recruits with acute gastroenteritis. Partial sequence analysis of the RNA-dependent RNA polymerase gene revealed the presence of two major sub-genogroups, all of which were related to genogroup II of NoV. Serological analysis using recombinant antigens confirmed this observation. Local strains associated with a 1999 outbreak were closely related to GII-6 strains, while those identified later were very closely related to GII-4 strains. GII-4 strains were also associated with an outbreak in civilian nursing homes in Israel in 2002 and samples from this outbreak were included in this study for comparison. This is the first report describing the molecular properties of NoV strains associated with diarrhea-related morbidity in Israel.

Clinical Trials of Shigella Vaccines in Israel

Shigellosis or bacillary dysentery is caused by organisms belonging to genus Shigella, divided into four species (S. dysenteriae, S. boydii, S.flexneri and S. sonnei). With the exception of S. sonnei which has a single serotype, each species is divided into several serotypes according to the O-polysaccharide antigen of the cell wall (S. dysenteriae has 12 serotypes, S. flexneri has 6 serotypes, and S. boydii has 18 serotypes). Shigella spp. are invasive organisms that penetrate into the enterocytes of the colon epithelium, escape very quickly from the phagocytic vacuole and multiplicate intracellularly. Although non-motile, shigellae can move on an actin skeleton and spread to adjacent cells. The inflammatory process is usually limited to the lamina propria and does not involve the spread of Shigella deeper, into the submucosa. Pathogenesis in Shigella spp. is associated with a constellation of genes encoded on both the chromosome and a large 140 MDa virulence plasmid. These genes can be divided into two groups: regulatory genes and structural genes. The 140 MDa plasmid encodes for all the genes essential for invasion of Shigella into the epithelium of the colon. Regulatory genes are located on the virulence plasmid or on the chromosome.