In 1995, Salmonella Enteritidis (SE) cases in the state of Utah increased fivefold. Isolates were identified as phage type 4 (PT4). Risk factors and sources of infection were investigated in two case-control studies, a traceback of implicated foods, and environmental testing. Forty-three patients with sporadic infections and 86 controls were included in a case-control study of risk factors for infection. A follow-up case-control study of 25 case and 19 control restaurants patronized by case and control patients examined risks associated with restaurant practices. In the first case-control study, restaurant dining was associated with illness (P = 0·002). In the follow-up case-control study, case restaurants were likelier to use > 2000 eggs per week (P < 0·02), to pool eggs (P < 0·05), and to use eggs from cooperative ‘A’ (P < 0·009). Eggs implicated in separately investigated SE PT4 outbreaks were traced to cooperative ‘A’, and SE PT4 was cultured from one of the cooperative's five local farms. We conclude that SE PT4 transmitted by infected eggs from a single farm caused a fivefold increase in human infections in Utah.

In June 1998, an increased number of persons with Salmonella blockley infection were reported from one German state. Because S. blockley is extremely uncommon in Germany, a case-control study was performed in order to find the source. A total of 13 patients met the case definition. Nine of 12 cases and 2 of 21 controls with food consumption histories reported eating smoked eel (OR 28·5; 95% CI 3·9–235·3). The consumed eel came from four different local smokeries, but could be traced back to fish farms in Italy. This outbreak indicates that eel may be a vehicle for salmonella infection and that the smoking process may not eliminate bacterial contamination from raw fish.

We report the first documented Campylobacter jejuni outbreak in an Austrian youth centre. Sixty-four children were involved of which 38 showed classical signs of campylobacter gastroenteritis. Since unpasteurized milk distributed by a local dairy was suspected to be the source of infection, stool samples were collected from 20 cows providing the milk. Five of the cows tested positive for C. jejuni. These isolates together with 37 clinical samples were compared by pulsed-field-gel electrophoresis (PFGE). The PFGE patterns, using the restriction endonucleases SmaI and SalI, were identical for the human and bovine isolates.This finding confirmed that the outbreak was caused by the consumption of unpasteurized milk contaminated with C. jejuni.

Active surveillance of Vibrio parahaemolyticus infection among hospitalized patients in Calcutta, India, showed the appearance of the O4[ratio ]K68 serovar for the first time in March 1998 alongside the continued predominant incidence of the O3[ratio ]K6 serovar. Strains belonging to both these serovars have been reported to possess pandemic potential. The genomes of O3[ratio ]K6 and O4[ratio ]K68 strains and for comparison, non-O3[ratio ]K6 and non-O4[ratio ]K68 strains isolated from two different countries, India and Thailand, were examined by different molecular techniques to determine their relatedness. The O3[ratio ]K6 and O4[ratio ]K68 strains from Calcutta and Bangkok carried the tdh gene but not the trh gene. Characterization of representative strains of these two serovars by ribotyping and by arbitrarily primed-polymerase chain reaction (AP-PCR) showed that the isolates had identical ribotype and DNA fingerprint. Pulsed-field gel electrophoresis (PFGE) performed with the same set of strains yielded nearly similar restriction fragment length polymorphism (RFLP) patterns for the O3[ratio ]K6 and O4[ratio ]K68 isolates from Calcutta and Thailand. Phylogenetic analysis of the NotI RFLP showed that the O3[ratio ]K6 and O4[ratio ]K68 strains formed a cluster with 78–91% similarity thus indicating close genetic relationship between the two different serovars isolated during the same time-frame but from widely separated geographical regions. The non-O3[ratio ]K6 and non-O4[ratio ]K68, in contrast, showed different ribotype, AP-PCR and PFGE patterns.

Eighty-four strains of Vibrio cholerae O1, O139 and non-O1/non-O139 from clinical and environmental sources were investigated for the presence of the toxin co-regulated pilus gene, tcpA, the virulence cassette genes ctxA, zot, ace and cep and also for their ability to elaborate haemolysin and protease. The ctxA and zot genes were detected using DNA–DNA hybridization while the ace, cep and tcpA genes were detected using PCR. Production of haemolysin and protease was detected using mammalian erythrocytes and an agar diffusion assay respectively. Analysis of their virulence profiles showed six different groups designated Type I to Type VI and the major distinguishing factor among these profiles was in the in vitro production of haemolysin and/or protease. Clinical O1, O139 and environmental O1 strains were similar with regard to presence of the virulence cassette genes. All environmental O1 strains with the exception of one were found to possess ctxA, zot and ace giving rise to the probability that these strains may actually be of clinical origin. One strain which had only cep but none of the toxin genes may be a true environmental isolate. The virulence cassette and colonization factor genes were absent in all non-O1/non-O139 environmental strains but production of both the haemolysin and protease was present, indicating that these may be putative virulence factors. These findings suggest that with regard to its pathogenic potential, only strains of the O1 and O139 serogroup that possess the tcpA gene which encodes the phage receptor, have the potential to acquire the CTX genetic element and become choleragenic.

Two models estimating the proportion of Escherichia coli O157[ratio ]H7 cases not reported in the Ontario notifiable diseases surveillance system are described. The first model is a linear series of adjustments in which the total number of reported cases is corrected by successive under-reporting coefficients. The structure of the second model is based on a relative difference in the proportion of E. coli O157[ratio ]H7 cases which are hospitalized between the surveillance database and the underlying population.

Based on this analysis, the rate of under-reporting of symptomatic cases of E. coli O157[ratio ]H7 infection in Ontario ranges from 78 to 88% corresponding to a ratio of 1 reported case for approximately 4–8 symptomatic cases missed by the surveillance system. This study highlights the need to increase awareness among public health workers of the potential biases that may exist in the interpretation of routine surveillance data.

Twenty verocytotoxigenic Escherichia coli (VTEC) O118 strains isolated between 1996 and 1998 from human patients in Germany were analysed for their serotypes, their virulence markers and their epidemiological relatedness. Three strains were typed as O118[ratio ]H12, these carried only the VT2d-Ount variant gene and were not associated with diarrhoea or haemolytic uraemic syndrome (HUS). Seventeen strains were serotyped as O118[ratio ]H16 or O118[ratio ]non-motile (NM). These carried all the genes for VT1, eae and EHEC-haemolysin. The O118[ratio ]H16/NM strains were from diarrhoea (13 cases) and HUS (2 cases). Sixteen of the patients were young infants and most infections were associated with a rural environment. Evidence for zoonotic transmission from cattle to humans was found in two cases. The epidemiological relationship between the human and bovine O118[ratio ]H16/NM isolates was indicated by homogeneous plasmid patterns and by very similar XbaI restriction patterns obtained by pulsed-field gel electrophoresis. VTEC O118[ratio ]H16/NM are emerging pathogens in Germany and should be classified as new enterohaemorrhagic E. coli (EHEC) types.

Shiga toxin (Stx)-producing Escherichia coli (STEC) strains isolated from a seagull in Japan were examined. A total of 50 faecal samples was collected on a harbour bank in Hokkaido, Japan, in July 1998. Two different STEC strains, whose serotypes were O136[ratio ]H16 and O153[ratio ]H− , were isolated from the same individual by PCR screening; both of them were confirmed by ELISA and Vero cell cytotoxicity assay to be producing active Stx2 and Stx1, respectively. They harboured large plasmids, but did not carry the haemolysin or eaeA genes of STEC O157[ratio ]H7. Based on their plasmid profiles, antibiotic resistance patterns, pulsed-field gel electrophoresis analysis (PFGE), and the stx genes sequences, the isolates were different. Phylogenic analysis of the deduced Stx amino acid sequences demonstrated that the Stx toxins of seagull-origin STEC were closely associated with those of the human-origin, but not those of other animal-origin STEC. In addition, Stx2Φ-K7 phage purified from O136 STEC resembled Stx2Φ-II from human-origin O157[ratio ]H7, and was able to convert non-toxigenic E. coli to STEC. These results suggest that birds may be one of the important carriers in terms of the distribution of STEC.

The number of band differences in DNA macrorestriction profiles required to distinguish unrelated strains from an index strain varies in an outbreak with the species and restriction enzyme used. In order to define this difference for epidemiological studies of Serratia marcescens, we produced DNA fingerprints from 57 isolates of the organism using the restriction enzyme XbaI and pulsed-field gel electrophoresis (PFGE). The isolates were selected on the basis of their epidemiology, serotype and phage-typing patterns to include 28 unrelated strains and 29 representatives from 2 distinct outbreaks. One of the outbreaks was prolonged, lasting for several years. Electrophoretic profiles consisting of 20 or more clearly resolved bands were obtained for all isolates. Twenty-six of the unrelated strains had unique profiles with over 10 band differences from all other strains, while 27 of the outbreak representatives could be assigned to the appropriate outbreak with confidence. The majority of the outbreak isolates had none or 2 band differences from the index profile, although 3 isolates differed by 5–7 bands. The 2 exceptions among the unrelated strains differed by 4 bands, and 3 phage typing reactions, and were isolated from London and Berlin 3 years apart, while the 2 exceptions among the outbreak collection had clearly unique profiles with over 20 band differences from each other and the outbreak profiles. Cluster analysis using Dice coefficient and UPGMA gave cut-off values of 75–78% similarity overall for related isolates, while the closest similarity for unrelated strains was 70%. The results of this study together with those of the 6 previous reports of PFGE for S. marcescens (which used either enzymes XbaI or SpeI) confirm that this technique is of value for this species and that with XbaI at least, most epidemiologically related strains will only differ by 3–4 bands. However, on occasion up to 7 band differences can be found within an apparent outbreak, which may be suggestive of genetic drift.

Klebsiella terrigena is very rarely isolated from humans; as yet, its clinical significance is uncertain. The aim of the present study was to evaluate whether this species is able to express putative virulence factors. A total of 72 faecal (n = 50) and clinical (n = 22) K. terrigena isolates was investigated and compared with faecal and clinical strains of K. pneumoniae. Mannose-sensitive haemagglutination (MSHA) was observed less often in K. terrigena (64–74%) than in K. pneumoniae strains. In contrast, the incidence of mannose-resistant haemagglutinin indicative of type 3 pili (MR/K-HA) (77–94%), serum resistance properties (10–23%), and production of enterobactin (100%) was similar in both species. None of the K. terrigena isolates were able to synthesize aerobactin; however, the frequency of aerobactin synthesis in K. pneumoniae was also only 5%. Serotyping showed capsular types K5 and K70 to be predominant. The virulence-associated serotype K2 was common in both K. terrigena and K. pneumoniae isolates. Taken together, the present results suggest that K. terrigena and K. pneumoniae are indistinguishable with respect to the expression of virulence factors.

In early 1992 we identified an outbreak of cryptosporidiosis in Oregon and sought to identify and control its source. We used a series of studies to identify risk factors for illness : (i) a case-control study among employees of a long-term-care facility (LTCF); (ii) a matched case-control study of the general community; (iii) a cohort study of wedding attendees; and (iv) a cross-sectional survey of the general community. Drinking Talent water was associated with illness in the LTCF (OR = 22·7, 95% CI = 2·7–1009·0), and in the community (matched OR = 9·5, 95% CI 2·3–84·1). Drinking Talent water was associated with illness only among non-Talent residents who attended the wedding (P < 0·001) and in the community (RR = 6·5, 95% CI 3·3–12·9). The outbreak was caused by contaminated municipal water from Talent in the absence of a discernible outbreak among Talent residents, suggesting persons exposed to contaminated water may develop immunity to cryptosporidiosis.

In April 1997, a large city in the northeastern United States changed their drinking water treatment practices. The city, which previously provided only chlorination for their surface water sources added filtration in addition to chlorination. To assess whether Cryptosporidium infections rates declined following filtration, we tested serological responses to 15/17-kDa and 27-kDa Cryptosporidium antigens among 107 community college students 1 month before and 225 students 5 months after filtration. Results suggest that levels of Cryptosporidium infections did not decline following water filtration. However, seasonal changes in other exposures may have confounded the findings. Swimming in a lake, stream or public pool and drinking untreated water from a lake or stream predicted a more intense response to one or both markers. Residence in the city, not drinking city tap water or drinking bottled water, gender, travel or exposure to pets, young pets, diapers or a household child in day care were not found to be predictive of more or less intense serological responses for either the 15/17-kDa and 27-kDa antigen.

A protracted outbreak of Norwalk-like virus (NLV)-associated gastroenteritis occurred in a large hotel in North-West England between January and May 1996. We investigated the pattern of environmental contamination with NLV in the hotel during and after the outbreak. In the ninth week, 144 environmental swabs taken from around the hotel were tested for NLV by nested RT–PCR. The sites were categorized according to the likelihood of direct contamination with vomit/faeces. The highest proportion of positive samples were detected in directly contaminated carpets, but amplicons were detected in sites above 1·5 m which are unlikely to have been contaminated directly. The trend in positivity of different sites paralleled the diminishing likelihood of direct contamination. A second environmental investigation of the same sites 5 months after the outbreak had finished were all negative by RT–PCR. This study demonstrates for the first time the extent of environmental contamination that may occur during a large NLV outbreak.

Carriage of Neisseria lactamica among household contacts of meningococcal disease (MCD) cases was investigated during an epidemic in Auckland, New Zealand. The overall carriage rate for N. lactamica was 10·5% (95% CI 7·4–13·5%) with a peak carriage rate in 2-year-olds of 61·5% (95% CI 26·6–88·1%). Factors associated with a significant (P < 0·05) increase in the likelihood of carriage included runny nose, the number of people per bedroom and youth. Genetic analysis of isolates revealed a striking correlation of strains within the same household but a high level of diversity between households, suggesting that household contact is an important factor in acquisition. For household contacts aged less than 5 years, there was a higher rate of carriage amongst those in contact with MCD cases under 8 years old than for contacts of cases aged 8 years and over. It is likely that development of MCD is a reflection of the nature and intensity of the exposure to a virulent strain of N. meningitidis, coupled with an absence of host resistance among those individuals not carrying N. lactamica.

This study evaluated whether a correlation exists between carriage of corynebacteria and the lack of immunity to diphtheria toxoid. Samples of both nasal and pharyngeal secretions were taken from 500 apparently healthy subjects of both sexes and of all ages and inoculated onto Tinsdale's medium. A serum sample was also taken for ELISA test to determine the titre of diphtheria toxin antibodies. None of the subjects carried Corynebacterium diphtheriae. Ninety-three strains of Corynebacterium spp. were isolated from 93 subjects and 86 of these were classified to species or group level by biochemical tests. C. xerosis was the most common (25·8%) followed by C. pseudodiphthericum (16·1%), C. jeikeium and C. striatum (both 10·8%), and C. urealyticum (9·7%). Three other species accounted for approximately 20% of strains and seven were unclassified as biochemically atypical corynebacteria. Non-protective antibodies to diphtheria toxin were found in 80 of the 93 subjects and a strong statistical association was demonstrated between carriage of corynebacteria and non-protective levels of anti-toxin antibodies. The remaining 13 subjects had protective levels of antitoxin antibodies. In contrast, only 45 of the 407 non-colonized subjects had non-protective antitoxin titres. The prevalence of carriage increased with age among males as did the percentage of non-protected subjects. The prevalence of female carriers of corynebacteria was significantly lower. Serum samples from 12 subjects with different antibody titres to diphtheria toxoid reacted to varying degrees with whole-cell lysates of a number of species of corynebacteria. The results suggest that a causal relationship may exist between nasopharyngeal carriage of corynebacteria and a low anti-diphtheria toxin immune response.

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 [les ] 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.

The ESEN (European Sero-Epidemiology Network) project was established to harmonize the seroepidemiology of five vaccine preventable infections including measles, mumps and rubella in eight European countries. This involved achieving comparability both in the assay results from testing in different centres and also sampling methodology. Standardization of enzyme immunoassay results was achieved through the development of common panels of sera by designated reference centres. The panels were tested at the reference laboratory and then distributed to each participating laboratory for testing using their routine methods. Standardization equations were calculated by regressing the quantitative results against those of the reference laboratory. Our study found large differences in unitage between participants, despite all using an EIA method standardized against an international or local standard. Moreover, our methodology adjusted for this difference. These standardization equations will be used to convert the results of main serosurvey testing into the reference country unitage to ensure inter-country comparability.

Data were collected on 6578 patients diagnosed with AIDS at 52 clinical centres in 17 European countries during an 11-year period from 1979 to 1989. The centres were divided into four regions, North, Central, Southeast, and Southwest. Differences in the incidence of most AIDS-defining opportunistic infections and malignancies were found. After adjusting for known possible confounders, statistically significant differences between regions remained. Pneumocystis carinii pneumonia (PCP) was more common in Northern Europe, Kaposi's sarcoma and toxoplasmosis in Central Europe, cytomegalovirus retinitis in South-eastern Europe, and extrapulmonary tuberculosis in South-western Europe. These differences we attribute primarily to different degrees of exposure to the respective underlying pathogens. The prevalence of these and other micro-organisms will determine the clinical course of HIV infections in parts of Eastern Europe and elsewhere where the virus now is spreading.

Drug use is a major mode of HIV transmission in Thailand. This study determined HIV incidence rates among drug users in a regional drug treatment centre in northern Thailand. A retrospective cohort of repeatedly-hospitalized drug users between 1993 and 1997 was formed and HIV incidence rates were calculated. The overall incidence was 11·44 per 100 person-years of observation. Gender, age, religion, ethnicity, education, employment, income, reasons for drug use, type of drugs, mode of use, spending on drugs, and referral for treatment are associated with HIV incidence. However, there are no associations between HIV incidence and history of treatment and mode of discharge from the centre. This implies that current treatment modality has no impact on HIV infection risk and other therapeutic approaches should be explored.

HIV and HTLV seroprevalence was determined by means of unlinked anonymous testing of 2144 sera, originally obtained from primary care patients by representative sampling of the Spanish population aged 15-39 years in 1996. HIV-1 seroprevalence was 4·3 per 1000 population in the 15–39 years age group [95% confidence interval (CI), 1·5–10·7] and 5·6 per 1000 (95% CI, 1·8–15·3) in the 20–39 years age group. Seroprevalence proved higher in males and urban residents. No antibodies to HIV-2 and HTLV-I were detected in any of the sera studied. However, presence of antibodies to HTLV-II was confirmed in one serum sample, while HTLV seroreactivity, though detected in another, could not be typed. The two HTLV-positive results equated to a seroprevalence of 1·9 per 1000 in the 20–39 years age group (95% CI, 0·3–8·6). HIV-1 seroprevalence was consistent with previous estimates yielded by back-calculation. The level of HTLV seroprevalence found suggests endemicity.