A multistate, foodborne outbreak of hepatitis A. National Hepatitis A Investigation Team.
BACKGROUND: We investigated a large, foodborne outbreak of hepatitis A that occurred in February and March 1997 in Michigan and then extended the investigation to determine whether it was related to sporadic cases reported in other states among persons who had consumed frozen strawberries, the food suspected of causing the outbreak. METHODS: The cases of hepatitis A were serologically confirmed. Epidemiologic studies were conducted in the two states with sufficient numbers of cases, Michigan and Maine. Hepatitis A virus RNA detected in clinical specimens was sequenced to determine the relatedness of the virus from outbreak-related cases and other cases. RESULTS: A total of 213 cases of hepatitis A were reported from 23 schools in Michigan and 29 cases from 13 schools in Maine, with the median rate of attack ranging from 0.2 to 14 percent. Hepatitis A was associated with the consumption of frozen strawberries in a case-control study (odds ratio for the disease, 8.3; 95 percent confidence interval, 2.1 to 33) and a cohort study (relative risk of infection, 7.5; 95 percent confidence interval, 1.1 to 53) in Michigan and in a case-control study in Maine (odds ratio for infection, 3.4; 95 percent confidence interval, 1.0 to 14). The genetic sequences of viruses from 126 patients in Michigan and Maine were identical to one another and to those from 5 patients in Wisconsin and 7 patients in Arizona, all of whom attended schools where frozen strawberries from the same processor had been served, and to those in 2 patients from Louisiana, both of whom had consumed commercially prepared products containing frozen strawberries from the same processor. CONCLUSIONS: We describe a large outbreak of hepatitis A in Michigan that was associated with the consumption of frozen strawberries. We found apparently sporadic cases in other states that could be linked to the same source by viral genetic analysis. (+info)
Immunosurveillance and the evaluation of national immunization programmes: a population-based approach.
Mass vaccination can change the epidemiological dynamics of infectious diseases. It may result in a limited persistence of natural and vaccine-induced immunity and a higher mean age of infection, which may lead to a greater risk of complications. The epidemiological situation should be monitored and immunosurveillance based on the assessment of specific antibodies against vaccine-preventable diseases in human serum is one of the tools. In order to estimate the immunity of the Dutch population reliably, a large-scale, population-based, collection of serum samples was established (8359 sera in a nation-wide sampling and 1589 sera from municipalities with low vaccine coverage). In contrast to collecting residual sera from laboratories, this approach gains extensive information by means of a questionnaire regarding the determinants of the immune status and the risk factors for the transmission of infectious diseases in general. The population-based approach gives a better guarantee that the data are representative than collecting sera from laboratories does. (+info)
Seroepidemiological evaluation of 1989-91 mass vaccination campaigns against measles, in Italy.
In 1989-91 anti-measles vaccination campaigns were conducted in several Italian regions to vaccinate all children aged between 13 months and 10-12 years without a history of measles or measles vaccination. This study was conducted to evaluate serological status after the mass vaccination campaigns. In 1994, capillary blood samples were collected from randomly selected children, aged 2-14 years, living in 13 local health units. Antibody titres were determined by ELISA. Blood spot samples were analysed for 4114 (75.6%) of 5440 selected children. Among the 835 that reported measles before 1990, 806 (96.5%) were immune and of the 2798 vaccinated, 2665 (95.2%) were immune. The Edmoston-Zagreb (E-Z) strain vaccine was associated with a lower level of immunity than the Schwarz (SW) strain. A history of measles identified almost all immune children. Vaccination with the SW strain conferred persistent immunity (at least 5 years) in 98% of vaccinees. The strategy was able to unite natural and induced immunity. (+info)
Prospective study of Chlamydia pneumoniae IgG seropositivity and risks of future myocardial infarction.
BACKGROUND: Chlamydia pneumoniae has been hypothesized to play a role in atherothrombosis. However, prospective data relating exposure to Chlamydia pneumoniae and risks of future myocardial infarction (MI) are sparse. METHODS AND RESULTS: In a prospective cohort of nearly 15 000 healthy men, we measured IgG antibodies directed against Chlamydia pneumoniae in blood samples collected at baseline from 343 study participants who subsequently reported a first MI and from an equal number of age- and smoking-matched control subjects who did not report vascular disease during a 12-year follow-up period. The proportion of study subjects with IgG antibodies directed against Chlamydia increased with age and cigarette consumption. However, prevalence rates of Chlamydia IgG seropositivity were virtually identical at baseline among men who subsequently reported first MI compared with age- and smoking-matched control subjects. Specifically, the relative risks of future MI associated with Chlamydia pneumoniae IgG titers >/=1:16, 1:32, 1:64, 1:128, and 1:256 were 1.1, 1.0, 1.1, 1.0, and 0.8, respectively (all probability values not significant). There was no association in analyses adjusted for other risk factors, evaluating early as compared with late events, or among nonsmokers. Further, there was no association between seropositivity and concentration of C-reactive protein, a marker of inflammation that predicts MI risk in this cohort. CONCLUSIONS: In a large-scale study of socioeconomically homogeneous men that controlled for age, smoking, and other cardiovascular risk factors, we found no evidence of association between Chlamydia pneumoniae IgG seropositivity and risks of future MI. (+info)
High seroprevalence of antibodies to human herpesvirus-8 in Egyptian children: evidence of nonsexual transmission.
BACKGROUND: In western countries, human herpesvirus-8 (HHV-8) appears to be transmitted mainly by sexual contact. To evaluate the role of other transmission routes, especially in developing countries, we estimated the seroprevalence of HHV-8 in Egyptian children, who, if seropositive, would have acquired the virus through a nonsexual route. METHODS: Sera from 196 children (<1-12 years of age), 20 adolescents (13-20 years of age), and 30 young adults (21-25 years of age) attending a vaccination program in Alexandria, Egypt, were studied. Immunofluorescence assays were used to detect antibodies against HHV-8 lytic-phase antigens (anti-lytic) and latent-phase antigens (anti-latent). Antibodies against Epstein-Barr virus viral cap antigen, cytomegalovirus, and HHV-6 were detected by enzyme-linked immunosorbent assays. Seroprevalence of these herpesviruses was calculated after stratifying the subjects by age. RESULTS: Anti-lytic and anti-latent HHV-8 antibodies were detected in 44.7% and 8.5% of the study participants, respectively. The prevalence of anti-lytic antibodies tended to increase with age, exceeding 50% in children older than 6 years; once children reached the age of 10 years, the prevalence tended to stabilize. The seroprevalence of other herpesviruses tended to be higher than that of HHV-8, ranging from approximately 83% to more than 97% in the 9- to 12-year age group. One- to 3-year-old children had higher titers of antilytic HHV-8 antibodies than children in the other age groups. Anti-latent antibodies were more frequently detected in individuals with high anti-lytic antibody titers. CONCLUSIONS: HHV-8 antibodies are highly prevalent in Egyptian children, suggesting that, in developing countries, HHV-8 infection may be acquired early in life through routes other than sexual transmission. The lower seroprevalence of HHV-8 relative to that of the other herpesviruses suggests that HHV-8 is less transmissible than other common herpesviruses. (+info)
Risk of Helicobacter pylori infection among long-term residents in developing countries.
The seroprevalence and incidence of Helicobacter pylori infection were determined among 312 North American missionaries who were serving in developing countries between 1967 and 1984. The majority (81%) resided in sub-Saharan Africa. When initially evaluated, the missionaries had a mean age of 40 years, 65% were female, and all were of white race/ethnicity. An ELISA showed that the initial prevalence of IgG antibody to H. pylori was 17%. After a mean of 7.4 years of service (1917 person-years of exposure), 37 (14%) of 259 initially seronegative subjects seroconverted to anti-H. pylori, giving an annual incidence of 1.9%. These data indicate a relatively higher risk of H. pylori infection among missionaries compared with an annual incidence of seroconversion of 0.3-1.0% in industrialized nations. Long-term residents in developing countries should be evaluated for H. pylori infection when gastrointestinal symptoms develop. (+info)
Age-specific decrease in seroprevalence of schistosomiasis in Puerto Rico.
In our previous work, we reported the first systematic, island-wide, serologic survey for schistosomiasis in Puerto Rico in 40 years. In that study, approximately 3,000 serum samples from the 76 municipalities comprising the island of Puerto Rico were tested for the detection of antibodies to S. mansoni microsomal antigens by the Falcon assay screening test-enzyme-linked immunosorbent assay (FAST-ELISA) and those positive were confirmed by an enzyme-linked immunoelectrotransfer blot (EITB). The highest EITB positivity was found in 17 municipalities, which comprised 48% of all seropositive samples. An additional finding was that 10% of the 215 EITB-positive samples were from individuals 25 years or younger and were for the most part of residents from the high seroprevalence areas. Thus, for this study we focused on 766 individuals 25 years of age or younger (45.5% males and 54.4% females), two-thirds of which were from 10 municipalities with the highest EITB seropositivity, and one-third from the 10 municipalities with the lowest EITB seropositivity found in our previous study. Of all samples, the results showed an overall FAST-ELISA positivity of 11.6%, with males similar to females (12.6 versus 10.7%, respectively). Confirmation by EITB was only 1.8%, with a males three-fold higher than females (3% versus 0.7%). When seropositivity was measured by age in five-year increments, a clear age-specific decrease in seropositivity was observed. Thus, by FAST-ELISA, 16.7% of the 21-25-year-old age group was positive, decreasing to 14.6%, 9.9%, 7.9%, and 9.3% in the 16-20-, 11-15-, 6-10-, and 1-5-year-old age groups, respectively. Confirmatory EITB showed even more impressive results: 4.7%, 2.6%, 1.2%, 0.7%, and 0% in the same age brackets. With regard to the high prevalence municipalities, only four of 10 (11 of 228 = 4.8%) had confirmatory EITB-positive samples and most were from municipalities of the Rio Grande de Loiza River basin and tributaries. The male to female positivity ratio was 4:1. Of the low prevalence municipalities, only single positive cases (by EITB) were found in three disperse municipalities. These results support the concept that there has been little transmission of S. mansoni in Puerto Rico during the first half of the 1990s and confirms anecdotal comments of local physicians who have seen virtually no new infections during the past three years. This makes the documentation of eradication of schistosomiasis from Puerto Rico feasible, a goal that should be set as being before the 100th anniversary of its discovery on the island by Isaac Gonzalez-Martinez in 1904. (+info)
Detection of antibody to avian influenza A (H5N1) virus in human serum by using a combination of serologic assays.
From May to December 1997, 18 cases of mild to severe respiratory illness caused by avian influenza A (H5N1) viruses were identified in Hong Kong. The emergence of an avian virus in the human population prompted an epidemiological investigation to determine the extent of human-to-human transmission of the virus and risk factors associated with infection. The hemagglutination inhibition (HI) assay, the standard method for serologic detection of influenza virus infection in humans, has been shown to be less sensitive for the detection of antibodies induced by avian influenza viruses. Therefore, we developed a more sensitive microneutralization assay to detect antibodies to avian influenza in humans. Direct comparison of an HI assay and the microneutralization assay demonstrated that the latter was substantially more sensitive in detecting human antibodies to H5N1 virus in infected individuals. An H5-specific indirect enzyme-linked immunosorbent assay (ELISA) was also established to test children's sera. The sensitivity and specificity of the microneutralization assay were compared with those of an H5-specific indirect ELISA. When combined with a confirmatory H5-specific Western blot test, the specificities of both assays were improved. Maximum sensitivity (80%) and specificity (96%) for the detection of anti-H5 antibody in adults aged 18 to 59 years were achieved by using the microneutralization assay combined with Western blotting. Maximum sensitivity (100%) and specificity (100%) in detecting anti-H5 antibody in sera obtained from children less than 15 years of age were achieved by using ELISA combined with Western blotting. This new test algorithm is being used for the seroepidemiologic investigations of the avian H5N1 influenza outbreak. (+info)