The HIV/AIDS epidemics among drug injectors: a study of contact structure through a mathematical model

Numerical results of a model with variable infectivity for the dynamics of HIV/AIDS (human immunodeficiency virus/acquired immune deficiency syndrome) have been compared with the data of AIDS cases among intravenous drug users in Italy, especially in the Latium region. We examined several hypotheses about the dynamics of the epidemics; for each we obtained, mainly through a least-square approach but also minimizing a different quantity, a best-fit estimate of the parameters. In the simplest model, the population is assumed to be homogeneous, and we estimate contact rate and year of start of the epidemics, obtaining a good fit up to 1989, less so after. A substantial increase in fit is obtained in assuming either a decrease of the contact rate over time or a heterogeneous population with a smaller active group. We have also compared models with different infectivity curves during the incubation period: the assumption of constant infectivity is untenable, whereas the often suggested hypothesis of a peak in infectivity shortly after infection seems to be in agreement with data.     

Sensitivity, specificity and predictive values of health service based indicators for the surveillance of influenza A epidemics

BACKGROUND: The Regional Influenza Surveillance Group (GROG) is a French surveillance network set up in 1984. It collects virological specimens and health service based indicators on a weekly basis. Our aim was to assess the predictive value of the health service based indicators for the detection of influenza A epidemics. METHODS: Virological data were used as a gold standard for defining the epidemics. For each health service based indicator, a statistical threshold was used as a test for the identification of epidemic weeks. Finally, an epidemiological criterion was defined in order to improve the specificity and the speed of detection of outbreaks. RESULTS: Health service based indicators have a positive predictive value of around 0.80. They also advance the detection of outbreaks by between 1 and 4 weeks. CONCLUSIONS: These indicators are easy to collect and are useful for the surveillance of influenza epidemics. Such a system is the prerequisite for the rational use of preventive tools.     

Mathematical model for the AIDS epidemic's evolution in Romania

The individuals are distributed in 9 risk groups (adults and children), in which an HIV transmission way is predominant. Taking into account a simplified graph of the HIV infection evolution, kinetic equations for the number of individuals from each risk group--situated in various stages of HIV infection--are written. The approximative solutions of these equations give us: the characteristic exponents of the temporal evolutions of the main and secondary local epidemics; the ratios Ci/Bi and Di/Bi of asymptomatically contaminated and dead (as consequence of AIDS)--versus symptomatically contaminated; the onset of local epidemics in various risk groups; the relative amplitude of the secondary local epidemics versus the main local ones.     

The new features of meningococcal meningitis (author's transl)

According to a previous pattern epidemics of meningococcal meningitis (MM) were localized in North tropical Africa, caused by A serotype, easily treated with sulfanilamides and prevented by a polyosidic vaccine, A type. Changes have occured : epidemics in Finland and Brazil, with an African A type germ, in place of the American, sulfa-resistant, C type; outburst of epidemics in South tropical Africa; presence of C type in Tchad, Niger and Nigeria. In the same time dramatic evolutions due to endotoxinic processes and drug-resistances are more frequently observed.     

Empirical determinants of measles metapopulation dynamics in England and Wales

A key issue in metapopulation dynamics is the relative impact of internal patch dynamics and coupling between patches. This problem can be addressed by analysing large spatiotemporal data sets, recording the local and global dynamics of metapopulations. In this paper, we analyse the dynamics of measles meta-populations in a large spatiotemporal case notification data set, collected during the pre-vaccination era in England and Wales. Specifically, we use generalized linear statistical models to quantify the relative importance of local influences (birth rate and population size) and regional coupling on local epidemic dynamics. Apart from the proportional effect of local population size on case totals, the models indicate patterns of local and regional dynamic influences which depend on the current state of epidemics. Birth rate and geographic coupling are not associated with the size of major epidemics. By contrast, minor epidemics--and especially the incidence of local extinction of infection--are influenced both by birth rate and geographical coupling. Birth rate at a lag of four years provides the best fit, reflecting the delayed recruitment of susceptibles to school cohorts. A hierarchical index of spatial coupling to large centres provides the best spatial model. The model also indicates that minor epidemics and extinction patterns are more strongly influenced by this regional effect than the local impact of birth rate.     

The effect of random vaccine response on the vaccination coverage required to prevent epidemics

The response people have to vaccination varies because their immune systems differ and vaccine failures occur. Here we consider the effect that a random response, independent for each vaccinee, has on the vaccination coverage required to prevent epidemics in a large community. For a community of uniformly mixing individuals an explicit expression is found for the critical vaccination coverage (CVC) and the effect of the vaccine response is determined entirely by the mean E(AB), where A and B, respectively, reflect the infectivity and susceptibility of a vaccinated individual. This result shows that the usual concept of vaccine efficacy, which focuses on the amount of protection the vaccine provides the vaccinee against infection, is not adequate to describe the requirements for preventing epidemics when vaccination affect infectivity. The estimation of E(AB) poses a problem because A and B refer to the vaccine response of the same individual. Similar results are found when there are different types of individual, but now the mean E(AB) may differ between types. However, for a community made up of households it is shown that the CVC also depends on other characteristics of the vaccine response distribution. In practice this means that estimating a single measure of vaccine effectiveness is generally not enough to determine the CVC. For a specific community of households it is found that the vaccination coverage required to prevent epidemics decreases as the variation in the vaccine response increases.     

Carcinoid of the major duodenal papilla

As demonstrated on the basis of clinico-epidemiological diagnostics, large epidemics of viral hepatitis (VH), earlier considered to be the epidemics of VHA, were in reality epidemics of VHE. Such epidemics originated due to the influence of the water factor and were called forth by the drying-up of rivers in Central Asia, which played an important role in their appearance. In combination with unusually high average monthly temperatures, especially in spring and summer, this is an important sign for the prognostication of new water epidemics of VHE.     

History of sleeping sickness in East Africa

The history of human sleeping sickness in East Africa is characterized by the appearance of disease epidemics interspersed by long periods of endemicity. Despite the presence of the tsetse fly in large areas of East Africa, these epidemics tend to occur multiply in specific regions or foci rather than spreading over vast areas. Many theories have been proposed to explain this phenomenon, but recent molecular approaches and detailed analyses of epidemics have highlighted the stability of human-infective trypanosome strains within these foci. The new molecular data, taken alongside the history and biology of human sleeping sickness, are beginning to highlight the important factors involved in the generation of epidemics. Specific, human-infective trypanosome strains may be associated with each focus, which, in the presence of the right conditions, can be responsible for the generation of an epidemic. Changes in agricultural practice, favoring the presence of tsetse flies, and the important contribution of domestic animals as a reservoir for the parasite are key factors in the maintenance of such epidemics. This review examines the contribution of molecular and genetic data to our understanding of the epidemiology and history of human sleeping sickness in East Africa.     

Acute asthma epidemics, weather and pollen in England, 1987-1994

Recent epidemics of acute asthma have caused speculation that, if their causes were known, early warnings might be feasible. In particular, some epidemics seemed to be associated with thunderstorms. We wondered what risk factors predicting epidemics could be identified. Daily asthma admissions counts during 1987-1994, for two age groups (0-14 yrs and > or = 15 yrs), were measured using the Hospital Episodes System (HES). Epidemics were defined as combinations of date, age group and English Regional Health Authority (RHA) with exceptionally high asthma admission counts compared to the predictions of a log-linear autoregression model. They were compared with control days 1 week before and afterwards, regarding seven meteorological variables and 5 day average pollen counts for four species. Fifty six asthma epidemics were identified. The mean density of sferics (lightning flashes), temperature and rainfall on epidemic days were greater than those on control days. High sferics densities were overrepresented in epidemics. Simultaneously high sferics and grass pollen further increased the probability of an epidemic, but only to 15% (95% confidence interval 2-45%). Two thirds of epidemics were not preceded by thunderstorms. Thunderstorms and high grass pollen levels precede asthma epidemics more often than expected by chance. However, most epidemics are not associated with thunderstorms or unusual weather conditions, and most thunderstorms, even following high grass pollen levels, do not precede epidemics. An early warning system based on the indicators examined here would, therefore, detect few epidemics and generate an unacceptably high rate of false alarms.     

On the critical behaviour of simple epidemics

We show how ideas and models which were originally introduced to gain an understanding of critical phenomena can be used to interpret the dynamics of epidemics of communicable disease in real populations. Specifically, we present an analysis of the dynamics of disease outbreaks for three common communicable infections from a small isolated island population. The strongly fluctuating nature of the temporal incidence of disease is captured by the model, and comparisons between exponents calculated from the data and from simulations are made. A forest-fire model with sparks is used to classify the observed scaling dynamics of the epidemics and provides a unified picture of the epidemiology which conventional epidemiological analysis is unable to reproduce. This study suggests that power-law scaling can emerge in natural systems when they are driven on widely separated time-scales, in accordance with recent analytic renormalization group calculations.     

Effect of training on general practitioners'' use of a brief intervention for excessive drinkers

During recent years the outcome of acute hepatitis A in chronic liver disease has been discussed controversially. Data from large hepatitis A epidemics and surveillance data from the United States suggest a significantly higher risk of fatal outcome in patients with chronic hepatitis B. Patients with chronic active hepatitis or liver cirrhosis seem to be at highest risk, while HBsAg carriers may exhibit a benign course of the disease. Patients with chronic hepatitis C also seem to have a significantly higher risk of fulminant hepatic failure when superinfected with hepatitis A. The recently reported unsuspected coincidence of autoimmune markers with a fulminant course of hepatitis A in those patients needs to be confirmed. Vaccination against hepatitis A in patients with chronic liver disease has been shown to be safe and effective.     

Experience of hepatitis A vaccination during an outbreak in a nursery school of Tuscany, Italy

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.     

Antigenic and genomic diversity of central European respiratory syncytial virus strains

Thirty-two RSV strains recovered during the winter months of 1987/88 to 1993/94 from hospitalized children in Vienna, Austria and Zagreb, Croatia were analysed for antigenic and genetic variations. Twenty-nine of the 32 isolates investigated belonged to group A and 3 to group B, with the majority of infections caused by subgroup A1 (21 of 29). Restriction endonuclease mapping of PCR products derived from parts of the N and G gene of 18 group A strains identified 3 distinct lineages, very similar to those defined by analysis of recurrent epidemics in Birmingham, United Kingdom during the same period. Results of this study provide further information on the global pattern of RSV and show that very similar viruses are present simultaneously in widely separated areas.     

Epidemiology of homicide in Allegheny County, Pennsylvania, between 1966-1974 and 1984-1993

BACKGROUND: We compared homicide death rates and characteristics of homicide victims and perpetrators in 1966-1974, 1984-1990, 1992-1993, and 1996 in Allegheny County, Pennsylvania, in an attempt to detect possible differences in the pattern of homicides. METHODS: Data were obtained from death certificates, coroner's records, police reports and newspapers. RESULTS: In the 1990s the homicide death rate increased for 15- to 24-year-old black men. The rate was 69 per 100,000/year for black men ages 15-24 years from 1966 to 1974 and rose to 275 per 100,000 from 1992 to 1993. Currently, the rates appear to be declining again. Preliminary data from 1996 showed the number of homicide deaths excluding vehicular homicides between 1993 and 1996 to decline from 19 to 8 for white men, from 70 to 42 for black men, from 9 to 3 for white women, and from 13 to 6 for black women with little change in the population (denominator). The dramatic drop from 111 to 61 deaths over a short time is similar to changes across the United State and is characteristic of epidemic rise and fall of homicides in the community. CONCLUSIONS: Between 1966 and 1993 Allegheny County experienced two separate homicide epidemics, one between 1966 and 1976 and the other between 1990 and 1993. Epidemics of homicide occur frequently and have different characteristics. New characteristics of the most recent epidemic of homicide include more homicides out of home, among strangers; less association with alcohol; and multiple perpetrators. Drug-use-associated homicides have also increased. Guns are the primary agents of homicide epidemics.     

Epidemic of influenza in Kyushu-Okinawa District (April 1994-March 1995)

The prevalence of influenza in Kyushu-Okinawa District in April 1994- March 1995 was studied as the prevalence of influenza virus, to determine the sero-type of influenza viruses isolated in Kyushu- Okinawa District prefectures and cities. As a result, three sero-types of influenza viruses, i.e. type A/H1N1, type H3N2 and type B, were isolated in Kyushu-Okinawa District in this season, but most of the isolates were type A/H3N2 and type B. Weekly changes of reported influenza patients and period of virus isolation at local public health institutes revealed that influenza epidemics of the earlier part in this season was caused by type A/H3N2 and the latter part due to type B. Type A/H3N2 spread all over Kyushu-Okinawa District in a shorter period (about 2 weeks) through the westside of Kyushu and down south, and type B stayed about one month in northern Kyushu and took about 7 weeks to spread all over Kyushu-Okinawa District. Based on these results, the spread of influenza virus in Kyushu-Okinawa District was visualized on the isopleth maps.     

Acalculous acute cholecystitis in leukemia

Alcaligenes xylosoxidans is an uncommon but serious cause of nosocomial epidemics. This report describes a cluster of two patients who underwent revision of hip arthroplasties and one patient who had a lumbar puncture. Cultures obtained during all three procedures showed A. xylosoxidans with similar antibiotic sensitivity patterns. An investigation found that saline used to process these specimens was contaminated with this organism.     

Infection prevention and control in the long-term-care facility. SHEA Long-Term-Care Committee and APIC Guidelines Committee

More than 1.5 million residents reside in US nursing homes. In recent years, the acuity of illness of nursing home residents has increased. Long-term-care facility residents have a risk of developing nosocomial infection that is similar to acute-care hospital patients. A great deal of information has been published concerning infections in the long-term-care facility, and infection control programs are nearly universal. This position paper reviews the literature on infections and infection control program in the long-term-care facility, covering such topics as tuberculosis, bloodborne pathogens, epidemics, isolation systems, immunization, and antibiotic-resistant bacteria. Recommendations are developed for long-term-care infection control programs based on interpretation of currently available evidence. The recommendations cover the structure and function of the infection control program, including surveillance, isolation, outbreak control, resident care, and employee health. Infection control resources also are presented.     

Stress (heat shock) proteins: molecular chaperones in cardiovascular biology and disease

Previously we have formulated transmission models of untreated tuberculosis epidemics (Blower et al., Nature, Medicine 1 (1995), 815-821); in this paper, we present time-dependent uncertainty and sensitivity analyses in order to quantitatively understand the transmission dynamics of tuberculosis epidemics in the absence of treatment. The time-dependent uncertainty analysis enabled us to evaluate the variability in the epidemiological outcome variables of the model during the progression of a tuberculosis epidemic. Calculated values (from the uncertainty analysis) for the disease incidence, disease prevalence, and mortality rates were approximately consistent with historical data. The time-dependent sensitivity analysis revealed that only a few of the model's input parameters significantly affected the severity of a tuberculosis epidemic; these parameters were the disease reactivation rate, the fraction of infected individuals who develop tuberculosis soon after infection, the number of individuals that an infectious individual infects per year, the disease death rate, and the population recruitment rate. Our analysis demonstrates that it is possible to improve our understanding of the behavior of tuberculosis epidemics by applying time-dependent uncertainty and sensitivity analysis to a transmission model.     

Diseases in European historical populations and their effects on individuals and society

Traditionally, populations are considered "historical" when first written evidences appear. Cultural development with all it's features--agricultural innovations and as a consequence--population growth, social specialisation and stratification, and finally--urbanisation trigger new environmental conditions, among them also in epidemiological situation, that have the feedback effects on the population and the individual. At this time only qualitative evaluations on many of questions can be presented. This paper is an attempt to synthesize available data on the following specific topics related to Medieval/Early Modern European population welfare: nutritional intake, malnutrition and famine; great epidemics and their consequences; spreading of specific infectious diseases (tuberculosis, syphilis, leprosy), which also had a great social resonance in those times, professional diseases. Considerations on their impact on demographical situation (life expectancy, birth rate), life quality and physical development and body build of an individual are also presented. Finally, possibilities for directional selection and impact on modern genetic diversity in Europe are discussed.