Using molecular techniques, we investigated whether the clone of Vibrio cholerae O1 biotype El Tor which appeared in Calcutta, India, in 1994 has spread to other cholera endemic areas in the country. The ribotype of 31 of the 33 strains isolated from different parts of India during 1996 and 1997 was identical to the ribotype displayed by the new clone of V. cholerae O1 which emerged in Calcutta in 1994. Likewise, 12 of the 15 strains examined by pulsed-field gel electrophoresis (PFGE) showed identical profile to that exhibited by the new clone of O1. The restriction fragment length polymorphism (RFLP) of CTX genetic element of these strains also matched with the new clone of O1 which emerged after the outbreak of V. cholerae O139 in Calcutta. However, two strains (AH042 and AH046) isolated from an outbreak in Ahmedabad (western India) showed different CTX RFLP but had the same ribotype and PFGE profile as the new clone, whereas one strain from Goa (G2) showed distinct ribotype and PFGE profile and the CTX RFLP was identical to the O1 strains which prevailed before the genesis of O139 in Calcutta. The drug resistance pattern of most of the O1 strains examined in this study, except strain G2, was similar to that of the new clone of V. cholerae O1. None of the strains in this study carried plasmids. Molecular studies clearly show that the new expanded drug resistant clone of V. cholerae O1 has spread to all cholera endemic areas in India and also provide evidence for the evolution of new clones of the O1 serogroup.

Six hundred and twenty-four Vibrio cholerae O1 strains, 623 serotype Ogawa and one serotype Inaba, isolated in Romania between 1977–95 were tested to detect all changing traits concerning serogroup, serotype, biotype, phage type and resistotype patterns and subsequently, the possible epidemiological relationship among these strains. Biotyping revealed one classical, 580 eltor strains and 43 intermediary variants. When tested with Mukerjee phages, 546 (87%) strains were sensitive and 78 (13%) resistant. One phage type (M4) dominated during 1977–90, two phage types (M4 and M5) exhibited the same high frequencies during 1991, a diversity of types occurred during 1993–4 whereas in 1995, two phage types (M4 and M5) showed similar distributions again. Five patterns of drug susceptibility were successively described during 1977–95. The most prominent changes in Vibrio cholerae O1 strains were noticed during 1993–4: the highest number of non-typable strains and intermediary variants, the widest spectrum of phage types and of multidrug resistance. In 1995, the strains reverted to the previous typable forms but a new drug resistance pattern was noticed.

Seventy clinical strains of Vibrio cholerae O1 isolated from 1982–96 in Samutsakorn, a port city 30 km southwest of Bangkok where cholera occurs at low levels with regular seasonality, were characterized to investigate if there were any differences among the O1 strains isolated before, during and after the O139 epidemic. Pulsed-field gel electrophoresis (PFGE) typing, ribotyping and southern blot hybridization with a cholera toxin probe (CT genotyping) demonstrated several genotypes among O1 strains isolated before the emergence of V. cholerae O139. However, O1 strains isolated during and after the advent of O139 showed identical ribotypes which were distinctly different from the types identified in strains isolated before the emergence of O139. Ribotypes identified in strains during and after the advent of O139 were also demonstrated by O1 strains isolated immediately before the emergence of O139. Considering the seasonality of cholera in Samutsakorn, the identical ribotype and CT genotype and the closely related PFGE types shown by all O1 strains isolated during and after the appearance of O139 is remarkable and suggest that the V. cholerae O1 strain may reemerge from an environmental source. A subgroup of V. cholerae O1 strains isolated before the emergence of the O139 epidemic had a ribotype identical to a type demonstrated by O139 strains isolated in Thailand. Our results support similar findings in Bangladesh and India that a distinct O1 strain appeared during the O139 epidemic. However, compared with the apparent identical strain which replaced O139 in Bangladesh and India, the emerged O1 strain in Samutsakorn showed a different ribotype and CT genotype.

We conducted a 1-year case-control study of sporadic vibrio infections to identify risk factors related to consumption of seafood products in two coastal areas of Louisiana and Texas. Twenty-six persons with sporadic vibrio infections and 77 matched controls were enrolled. Multivariate analysis revealed that crayfish (P<0·025) and raw oysters (P<0·009) were independently associated with illness. Species-specific analysis revealed an association between consumption of cooked crayfish and Vibrio parahemolyticus infection (or 9·24, P<0·05). No crayfish consumption was reported by persons with V. vulnificus infection. Although crayfish had been suspected as a vehicle for foodborne disease, this is the first time to our knowledge that consumption of cooked crayfish has been demonstrated to be associated with vibrio infection.

An outbreak of gastrointestinal illness affecting 12 of 29 customers of a ‘Hawaiian’ theme restaurant specializing in stir-fried food occurred in Cardiff, Wales in February 1997. Campylobacter jejuni serotype HS50 phage type 49 (PT49) was isolated from 5 cases. A total of 47 isolates of C. jejuni HS50 PT49 were identified from Wales during 1997, of which 11 were isolated in late February or early March and from the Cardiff area. In the outbreak, illness was associated with eating stir-fried chicken pieces (relative risk 4·81, 95% confidence interval (CI) 0·76–30·44, P=0·03) and a dose-response relationship between risk of illness and amount of chicken consumed was observed (χ2-test for linear trend 3·96, P=0·047). Undercooking of chicken was probably due to a combination of inadequate cooking time and use of large chicken pieces. This is the first time that stir-fried food has been associated with a campylobacter outbreak. The incident also illustrates the value of routine campylobacter subtyping in supporting outbreak investigation.

We report a foodborne outbreak of Campylobacter jejuni infection in a summer camp. Outbreak-related cases occurred in 79 persons including 3 secondary cases in campers. Campylobacter jejuni was isolated from stool specimens from 16 of 21 patients who submitted a sample; 13 viable isolates were serotyped and all were serotype O[ratio ]33 (somatic O scheme) or HL[ratio ]18 (heat-labile scheme), and biotype III (Lior scheme). This serotype is widely distributed geographically but rarely isolated from humans. Samples of water from the wells supplying the camp were negative for faecal coliforms, and raw milk had not been served in the camp. A matched (1[ratio ]1) case-control study identified tuna salad served for lunch on 19 July as the likely food item associated with illness (matched odds ratio=22; 95% confidence intervals (CI)=3·6–908). Swimming in the camp pool and other recreational water use in area lakes by the campers were not statistically associated with illness. The precise mechanism of introduction of the organism into the tuna salad remains unknown; contamination most likely occurred through cross-contamination with another food product, the hands of a food handler, or a work surface. Several deficiencies in the operation of the camp kitchen were identified. In Wisconsin, kitchens of such camps are subject to different inspection rules than restaurants. Camp staff, administrators, counselors, food managers, and infirmary staff, should fulfil important roles in their respective areas to prevent future outbreaks.

Molecular analyses based on plasmid profile typing and pulsed-field gel electrophoresis have defined a strain of Salmonella enterica serotype Anatum associated with the consumption of a particular brand of formula-dried milk responsible for an outbreak in late 1996/early 1997 involving 15 infants and 2 relatives in the UK, and 2 infants in France. The study has demonstrated the value of laboratory-based surveillance involving identification of the outbreak strain at the molecular level coupled with food microbiology and targeted epidemiological investigations, and has highlighted the importance of rapid communication and subsequent international collaboration through the European Union-funded Salm-Net salmonella surveillance network.

Experiments with 2 wild type isolates of Salmonella enterica serotype Enteritidis PT4, which differed in RpoS expression, tolerance to certain hostile environments and pathogenicity, found that changes in in vitro acid, heat, or peroxide tolerance had no effect on the ability of the isolates to multiply in the spleens of C57/BL7/J mice infected orally. Thus, with the pathogenic RpoS-positive isolate, the infectivity of log phase chilled cells, which are profoundly acid-sensitive, was the same as that of non-chilled stationary phase cells which are acid-tolerant. Similarity the infectivity of the RpoS-negative, sensitive isolate, was not enhanced by increases in any tolerance. The ability to survive on surfaces, like infectivity, was also largely unaffected by either growth phase or cold exposure. These two attributes may thus be related and, given that the pathogenic PT4 isolate is capable of prolonged survival and the non-pathogenic isolate survives poorly, survival could serve as a potential marker of pathogenicity. Although the pathogenicity of the two isolates was very different, they showed an almost identical increase in acid tolerance following culture at pH 4·0 for up to 60 min.

A total of 259 clinical isolates of nonrepetitive non-typhi salmonellae (NTS) were examined for antibiotic resistance patterns and plasmid content. The antibiotics used were amoxicillin-clavulanic acid (AMC), ampicillin (AM), aztreonam (ATM), carbenicillin (CB), cefixime (CFM), cefotaxime (CTX), cefoxitin (FOX), ceftazidime (CAZ), ceftriaxone (CRO), chloramphenicol (C), ciprofloxacin (CIP), gentamicin (GM), imipenem (IPM), ofloxacin (OFX), tetracycline (TE), trimethoprim-sulfomethoxazole (SXT). Multi-drug resistant (MDR) strains comprised 19·3% of the total isolates (50/259) and almost all were S. typhimurium (49/50). Fifteen different patterns of resistance was observed, AM/CB/C/AMC/TE and AM/CB/C/AMC/SXT/GM/CTX/CRO/CAZ/CFM/ATM being the most frequent patterns. Twenty-eight out of 50 multiresistant isolates were found to contain at least one plasmid (mean five) and the size of the plasmids ranged between 1·7 and 158 kb. Plasmid profiles of multi-resistant NTS strains were heterogenous as 21 different profiles were detected in a total of 28 plasmid-bearing isolates. No direct correlation was established between antibiotic resistance patterns and plasmid profiles.

The net and basic reproduction numbers are among the most widely-applied concepts in infectious disease epidemiology. A net reproduction number (the average number of secondary infectious cases resulting from each case in a given population) of above 1 is conventionally associated with an increase in incidence; the basic reproduction number (defined analogously for a ‘totally susceptible’ population) provides a standard measure of the ‘transmission potential’ of an infection. Using a model of the epidemiology of tuberculosis in England and Wales since 1900, we demonstrate that these measures are difficult to apply if disease can follow reinfection, and that they lose their conventional interpretations if important epidemiological parameters, such as the rate of contact between individuals, change over the time interval between successive cases in a chain of transmission (the serial interval).

The net reproduction number for tuberculosis in England and Wales appears to have been approximately 1 from 1900 until 1950, despite concurrent declines in morbidity and mortality rates, and it declined rapidly in the second half of this century. The basic reproduction number declined from about 3 in 1900, reached 2 by 1950, and first fell below 1 in about 1960. Reductions in effective contact between individuals over this period, measured in terms of the average number of individuals to whom each case could transmit the infection, meant that the conventional basic reproduction number measure (which does not consider subsequent changes in epidemiological parameters) for a given year failed to reflect the ‘actual transmission potential’ of the infection. This latter property is better described by a variant of the conventional measure which takes secular trends in contact into account. These results are relevant for the interpretation of trends in any infectious disease for which epidemiological parameters change over time periods comparable to the infectious period, incubation period or serial interval.

Liverpool, a seaport in NW England, suffered severely from lethal infectious diseases in the second half of the 19th century: the population was densely crowded and malnourished and life expectancy was low. Time-series analysis shows that the epidemics of whooping cough (i) had an interepidemic interval of 2·9 years, 1863–85, which lengthened to 3·4 years, 1885–1900 (ii) were strongly coherent with wheat prices (P<0·001) and (iii) also correlated with cycles of seasonal weather conditions. It is suggested from mathematical modelling that the epidemics in this compromised population were maintained (i.e. the system was driven) by an oscillation of malnutrition and by seasonal weather conditions. A model that incorporates both the dynamics of whooping cough and the demographic characteristics of the population is presented. It has been shown to replicate the dynamics of the epidemics and has been used to predict the changes with time of (i) the force of the infection and (ii) the proportion of those infected with whooping cough who died.

A multiethnic cohort of adult members of the Kaiser Permanente Medical Care Program (55300 men and 65271 women) was followed for 15 years (1979–93) to assess the association between total cholesterol and risk of infections (other than respiratory and HIV) diagnosed in the in-patient setting. Using multivariate Cox regression, total cholesterol was inversely and significantly related to urinary tract, venereal, musculo-skeletal, and all infections among men; and to urinary tract, all genito-urinary, septicaemia or bacteraemia, miscellaneous viral site unspecified, and all infections among women. The reduction of risk of all infections associated with a 1 s.d. increase in total cholesterol was 8% in both men (95% CI, 4–12%) and women (95% CI, 5–11%). For urinary tract infections among men, as for septicaemia or bacteraemia and nervous system infections among women, the risk relation was restricted to persons aged 55–89 years. Nervous system infections were positively related to total cholesterol among women aged 25–54. In both genders, the significant inverse association with all infections persisted after excluding the first 5 years of follow-up. Collectively, these data are suggestive of an inverse association, although not entirely consistent, between total cholesterol and incidence of infections either requiring hospitalization or acquired in the hospital. Further research is needed to elucidate whether these associations are biologically plausible or represent uncontrolled confounding by unmeasured risk factors.

A composite microporous membrane made of poly(N-benzyl-4-vinylpyridinium chloride) that showed strong affinity with bacterial cells was prepared as a filter material for removing airborne bacteria. Thickness, pore diameter and porosity of the membrane were 0·72 mm, 14·5 μm and 63%, respectively. Electron micrographic analysis revealed that the membrane consisted of a very large number of connected beads of 1·4 μm in diameter made of the pyridinium-type polymer. Filtration using the membrane was performed easily at low flow rates with insignificant pressure drop across the membrane. Filtration at 63·7 cm/sec gave 99·98% and 99·996% removal (3·7 and 4·4 log10-unit reduction in concentration) of Escherichia coli and Pseudomonas aeruginosa, respectively. Staphylococcus aureus was not detected in filtrates. Since pores of the membrane were much larger than these bacteria, the efficient removal was best explained in terms of the affinity of the polymer with bacterial cells.

We conducted a survey to determine the prevalence of known and theoretical exposure risks for cryptosporidiosis among selected New York City residents. Subjects were recruited from outpatients attending either a practice for persons with HIV infection (n=160), or other medical practices (n=153), at The New York Hospital–Cornell Medical Center. Despite a greater concern for waterborne infection, 82% of HIV-infected subjects reported consuming municipal tap water compared to 69% of subjects from other medical clinics (OR 2·1, 95% CI 1·2–3·6, P=0·006). Although 18% and 31% of subjects, respectively, denied any tap water consumption at home or work, all but one from each cohort responded positively to having at least one possible alternate source of tap water ingestion such as using tap water to brush teeth or drinking tap water offered in a restaurant. 78% and 76% of subjects, respectively, had at least one potential risk for exposure other than municipal water consumption, such as swimming in pools or contact with animals. Our findings indicate that it is possible to stratify the population into subsets by the amount of tap water consumed. This suggests that an observational epidemiologic study of the risk of contracting cryptosporidiosis from everyday tap water consumption is feasible.

The data of two cohort studies of HIV-infected individuals were used to examine whether the rate of CD4 decline is a determinant of HIV progression, independent of the most recent CD4 count. Time from seroconversion to clinical AIDS was the main outcome measure. Rates of CD4 decline were estimated using the ordinary least squares regression method. AIDS incidences were compared in individuals who had previously experienced either a steeper or a less steep rate of CD4 decline. Cox proportional hazards model including a time-dependent covariate for the rate of CD4 decline was performed. The rate of prior CD4 decline was significantly associated with the risk of developing AIDS independently from the most recent CD4 count, with a 2% increase in hazard of AIDS (P<·01) for a difference of 10 cells/mm3 in the estimated yearly drop in CD4 count. This finding gives scientific credit to the belief that individuals with a prior steeper CD4 decline consistently have a higher subsequent risk of developing AIDS than those with a less steep prior decline.

An outbreak of hepatitis A started in late October 1996 in a nursery school in Tuscany, Italy. A programme of hepatitis A vaccination without the use of immunoglobulin started at the beginning of December 1996 and included 33 children, 21 household contacts and 6 adults working in the school. Overall, 11 cases occurred in children attending the school (attack rate 27%) and 10 among their household contacts (attack rate 9%). The latter also included parents, and, in two cases, grandmothers. The data indicate that susceptibility to HAV has increased over recent decades in central Italy. Past and recent experience shows that the usual duration of hepatitis A epidemics in the absence of immune prophylaxis is longer than that described here. The use of hepatitis A vaccine probably contributed to the early extinction of the outbreak, because no further cases were notified in the area after 7 February 1997.

Data on injecting anabolic steroid users, within the national Unlinked Anonymous HIV Prevalence Monitoring Survey of injecting drug users (IDUs) were analysed to determine their risk of acquiring blood borne viruses. One hundred and forty-nine participants who had injected anabolic steroids in the previous month were identified from 1991–6, contributing 1·4% of all participation episodes in the survey. Rates of needle and syringe sharing by steroid users were low. Three of the 149 (2·0%) had anti-HBc and none had anti-HIV in their salivary specimens. The prevalence of anti-HBc in steroid injectors was significantly lower than in heroin injectors, 275/1509 (18%) (P<0·001), or in amphetamine injectors, 28/239 (12%) (P<0·001). The risk of blood borne virus transmission amongst these steroid injectors is low, probably due to hygienic use of injecting equipment and low levels of sharing. It is important to distinguish steroid injectors from other IDUs because they are a distinct group in terms of lifestyle and injecting practice.

Despite Department of Health recommendations, universal antenatal testing for hepatitis B virus (HBV) is not performed throughout Scotland. We describe the evaluation of an assay to document past or present infection with HBV, by identifying maternal antibody in routine Guthrie dried neonatal blood spot samples taken when infants are 7 days old. A modified haemagglutination assay to detect antibody to hepatitis B core antigen (CORECELL, Green Cross) was validated and found to be 79% sensitive (44/56) and 100% (105/105) specific when used with dried blood spot samples made from panels of serum of known reactivity. Ninety-three percent (13/14) of HBV carriers were CORECELL positive. Sixty-six (0·5%) of 14044 routine Guthrie samples taken from babies born in Scotland from June–August 1992 were CORECELL positive indicating past or present maternal infection with HBV. A cross-sectional survey would document the maternity hospitals where universal antenatal hepatitis B screening should be urgently established.

The present study examined the effect of hepatitis B virus (HBV) and alcohol intake, and the role of hepatitis delta virus (HDV) and hepatitis C virus (HCV) in the aetiology of chronic liver disease in Albania. A total of 106 cases of liver cirrhosis or chronic hepatitis were compared to 195 control patients without these or other liver diseases. Adjusted odds ratios were 52·7 (95% CI 22·7–122) for HBV surface antigen, 26·9 (95% CI 4·9–147) for anti-HCV, 26·2 (95% CI 3·1–221) for anti-HDV, 2.4 (95% CI 1·3–4·4) for lifetime alcohol intake and 2·3 (95% CI 1–5·5) for duration of alcohol intake. Although not significant, an interaction was suggested between HBsAg and anti-HCV and between HBsAg and alcohol intake. Our study underlines the role of hepatitis viruses in the development of chronic liver diseases. Additionally, it suggests that heavy alcohol intake may magnify the effect of HBV on these diseases. HBV vaccination and alcohol abstention appear to be important strategies to reduce the risk of liver cirrhosis and chronic hepatitis in Albania.

Epidemiological research on respiratory syncytial virus (RSV) infections in children was carried out at the Virology Laboratory, University Teaching Hospital (UTH), in Lusaka, Zambia, from January–December 1996. Specimens including 736 nasal washings and 2424 throat swabs were collected from children with acute respiratory infections (ARI) and tested for RSV by enzyme immunoassay and by virus isolation. RSV was isolated in 62 (4·1%) of 1496 throat swabs collected from March to September and was detected in 99 (16·3%) of 609 nasal washings from March to November. The average RSV isolation rate was 2·6% and the average RSV detection rate was 13·5%. The highest RSV isolation (8·1%) and detection (30·5%) rates were in June 1996. RSV antibody in the 278 serum specimens collected from Zambian children, who were hospitalized in the paediatric ward, UTH, was detected using a standard neutralization test. The antibody positive rate was 60–80% in children >4 years. It is evident that RSV is one of the main causal agents of ARI in children in Zambia.