A stochastic model for the development of an AIDS epidemic in a heterosexual population.

A non-age-dependent model, describing the evolution of a bisexual population, is developed in this paper and applied to projecting an AIDS epidemic in a heterosexual population. Included in the formulation are frequency- and non-frequency-dependent rules of partnership formation as well as five states of HIV disease, affecting the probability of infection per sexual contact. Results from computer experiments, designed to study the development of an AIDS epidemic in a heterosexual population fed by single males with a 50% prevalence of HIV infection prior to becoming active in heterosexual partnerships, are reported. In these experiments, the only source of HIV infection for females was sexual contacts with infected males within partnerships. Data on the probability of infection per sexual contact with an infected partner and the number of sexual contacts per month were incorporated into the model. However, the numbers used for the initial population of singles, couples, and those becoming sexually active per month were hypothetical. Even though the prevalence of HIV infection among males entering heterosexual partnerships was high, after 30 years the projected prevalence of HIV infection among females ranged from about 10 to 15% depending in part on the expected duration of partnerships and on whether the frequency- or non-frequency-dependent model was used. In these experiments, solutions of the embedded, nonlinear, deterministic equations for the incidence of HIV infection and the cumulative number of deaths due to AIDS proved to be good measures of central tendency for the sample functions of the stochastic population process.     

We rely on the common sense of young people

The principles of the primary prophylaxis, analogous to the program "Harm Reduction", are presented. The basis for placing this work on broad footing was the rapid assessment of the situation with the use of narcotic drugs in the city (the number of users exceeded 10,000 per 238,000 inhabitants) with a tendency towards a sharp decrease of the age of the users (9-13 years). The experience of work on the training of medical personnel, directly contacting with blood and thus considered to be a risk group, taking into account risky professional behavior (potentially dangerous), was accumulated. The training activities among students of medical schools proved to be effective. They became the best volunteers and leaders among young people. Adolescents aged 14-18 years were enlisted as volunteers: they worked in different places usually attended by young people and invited drug addicts to the anonymous examination room. The role of local mass media in educating the public on of the problems of the prevention of HIV infection is discussed. As a result, the activation of the youth movement in support of the program "Anti-AIDS" and an increase in the number of people in target groups coming to the anonymous examination room are noted.     

Morbidity and mortality in acute viral hepatitides in a hyperendemic region. The role of viral hepatitis E

Official annual statistical data on morbidity in acute viral hepatitides (AVH), including the number of lethal cases, for 1985-1995 were analyzed. Mortality rates per 100,000 of the population at the period of 11 years were calculated for different age groups, sex and the place of residence. 396 and 99 patients were examined for the presence of serological markers of hepatitides A, B and E, respectively, at the periods of epidemic rises in morbidity and satisfactory epidemic situation. In the course of 11 years AVH caused the death of 22,405 persons. In 1985-1987 the average mortality level (ML) reached 12.3-17.8 per 100,000 of the population (with morbidity being 1,200-1,400 and was essentially higher among the rural population in comparison with the urban population. During these years the highest ML, was registered among children aged 0-2 years (190-50 per 100,000) and, among adults, mainly among women aged 20-29 years (21.4-19.6 per 100,000). During the years when the epidemic of AVH was absent, ML among these groups was essentially lower: 40-20 among children aged 0-2 years and 4-5 among women aged 20-29 years. In 1987 in the Fergana Valley hepatitis E was detected in 72.2% of all examined patients, and in the southern areas of the country in 68.7%. A sharp rise on mortality among women of the productive age at the period of the epidemic rise of AVH morbidity in the endemic region indicated that this epidemic was linked with hepatitis E. High ML among young children may be indicative of a highly unfavorable course of hepatitis E in the group of infants, which had never been registered before. This newly established regularity may be used for the retrospective diagnostics of the outbreak of hepatitis E.     

Tuberculosis Mortality and Living Conditions in Bern,Switzerland, 1856-1950

Background

Tuberculosis (TB) is a poverty-related disease that is associated with poor living conditions. We studied TB mortality and living conditions in Bern between 1856 and 1950.

Methods

We analysed cause-specific mortality based on mortality registers certified by autopsies, and public health reports 1856 to 1950 from the city council of Bern.

Results

TB mortality was higher in the Black Quarter (550 per 100,000) and in the city centre (327 per 100,000), compared to the outskirts (209 per 100,000 in 1911–1915). TB mortality correlated positively with the number of persons per room (r = 0.69, p = 0.026), the percentage of rooms without sunlight (r = 0.72, p = 0.020), and negatively with the number of windows per apartment (r = -0.79, p = 0.007). TB mortality decreased 10-fold from 330 per 100,000 in 1856 to 33 per 100,000 in 1950, as housing conditions improved, indoor crowding decreased, and open-air schools, sanatoria, systematic tuberculin skin testing of school children and chest radiography screening were introduced.

Conclusions

Improved living conditions and public health measures may have contributed to the massive decline of the TB epidemic in the city of Bern even before effective antibiotic treatment became finally available in the 1950s.     

Improvement in the tactics of systematic gamma globulin prevention of viral hepatitis taking the morbidity prognosis into account]

On the example of 4 cites of the RSFSR under conditions of expected epidemic threat a possibility was shown of directed influence on the viral hepatitis A epidemic process of preseasonal gamma-globulin prophylaxis conducted in 90% of "organized" children, aged from 1 to 12 years. The dose used was 0.75 ml of a 10% preparation. The method of Gorky Institute of Epidemiology and Microbiology was used to prognosticate the morbidity. It is recommended to improve the tactics of preseasonal gamma-globulin prophylaxis with consideration to the data of the viral hepatitis prognosis.     

Methodological bases for the study and the patterns of the seasonality of viral hepatitis A

On the basis of the study of the data on the incidence of viral hepatitis A in one of the districts of a big city for 20 years the authors come to the conclusion on the advisability of a comparative study of the monthly changes in the incidence of hepatitis A within individual uniform morbidity cycles covering the periods of many years and the use of average monthly data for many years for plotting the typical curve, as well as the use of the simplified for the calculation of the upper limit of annual morbidity. Similarities and differences in the monthly dynamics of morbidity in the years of high and low morbidity levels have been revealed, and the age group of the population (20-39 years) which ensures the continuity of the epidemic process all the year round has been determined. The factors contributing to the seasonal activation of the epidemic process start operating in June among schoolchildren aged 11-14 years, and later their operation spreads to other groups of the population.     

Trends in abundance of tropical forest insects

Summary The stability of a large variety of insect populations was studied using 14 years of light-trap data collected in a relatively undisturbed tropical forest in Panama. Special emphasis was placed on trends in abundance over time. A large between-species variation was found in stability, ranging from nearly constant to violently fluctuating. Over a 14-year period 22% of the species with more than 26 individuals caught showed an average trend of more than 10% of their mean abundance per year, and 4% a trend of more than 20% per year. Even among the 78 species represented by more than 1000 individuals, 7 species, 9%, showed a trend of more than 10% of mean abundance per year. These results appear to be incompatible with the generally held tenet that natural populations in undisturbed environments fluctuate within rather narrow abundance limits, and may indicate that at least a certain proportion of natural populations are not kept within such limits by regulatory processes. Actual fluctuating patterns vary a great deal between species, suggesting the absence of some dominant environmental process affecting several species at the same time. The total number of species and individuals, and the associated value of the -diversity index remained at the same level over the 14 years.     

Mathematical Modeling of Hepatitis C Prevalence Reduction with Antiviral Treatment Scale-Up in Persons Who Inject Drugs in Metropolitan Chicago

Background/Aim

New direct-acting antivirals (DAAs) provide an opportunity to combat hepatitis C virus (HCV) infection in persons who inject drugs (PWID). Here we use a mathematical model to predict the impact of a DAA-treatment scale-up on HCV prevalence among PWID and the estimated cost in metropolitan Chicago.

Methods

To estimate the HCV antibody and HCV-RNA (chronic infection) prevalence among the metropolitan Chicago PWID population, we used empirical data from three large epidemiological studies. Cost of DAAs is assumed $50,000 per person.

Results

Approximately 32,000 PWID reside in metropolitan Chicago with an estimated HCV-RNA prevalence of 47% or 15,040 cases. Approximately 22,000 PWID (69% of the total PWID population) attend harm reduction (HR) programs, such as syringe exchange programs, and have an estimated HCV-RNA prevalence of 30%. There are about 11,000 young PWID (<30 years old) with an estimated HCV-RNA prevalence of 10% (PWID in these two subpopulations overlap). The model suggests that the following treatment scale-up is needed to reduce the baseline HCV-RNA prevalence by one-half over 10 years of treatment [cost per year, min-max in millions]: 35 per 1,000 [$50-$77] in the overall PWID population, 19 per 1,000 [$20-$26] for persons in HR programs, and 5 per 1,000 [$3-$4] for young PWID.

Conclusions

Treatment scale-up could dramatically reduce the prevalence of chronic HCV infection among PWID in Chicago, who are the main reservoir for on-going HCV transmission. Focusing treatment on PWID attending HR programs and/or young PWID could have a significant impact on HCV prevalence in these subpopulations at an attainable cost.     

The duality of the qualitative determinacy of the epidemic process in anthroponoses as the main trait distinguishing them from the epidemic manifestations of zoonotic diseases in man

The present article substantiates the necessity of defining more accurately the notion "epidemic process" and using this term only in reference to anthroponotic diseases. Proceeding from the philosophical concept of the qualitative definiteness of material objects and phenomena, the author proposes to distinguish the epidemic process in anthroponoses from mass spread of zoonotic diseases among humans on the basis of using the systemic qualities of the epidemic process, and in particular the principle of the dual character of the qualitative definiteness of objects and phenomena as the distinctive feature of the epidemic process of anthroponoses. Distinction, based on this principle, between anthroponotic diseases and zoonotic diseases in groups of humans must be reflected in the definitions of these phenomena. The application of the term "epidemic process" only in reference to anthroponotic diseases is proposed, while zoonotic diseases in groups of humans should be considered as epidemic manifestations of zoonotic infections.     

The general characteristics of the epidemic process and of the circulating streptococcal strains during an upsurge in scarlatina morbidity in Leningrad

The dynamics of scarlet fever morbidity in Leningrad for many years was studied and the absence of any effect produced by the existing system of preventive measures against this disease for the last 30 years was shown. On the basis of epidemiological and bacteriological data the authors came to the conclusion on the unity of the epidemic process of scarlet fever in the whole city and the relatively autonomous character of the process in individual districts. The necessity of the realization of epidemiological surveillance on streptococcal infection, with special emphasis on the multilevel social structure of the city and the wide use of the bacteriological diagnosis of streptococcal diseases, is substantiated.     

Assessment of the separate elements of an epidemiological overview of poliomyelitis today

The materials on the epidemiological supervision of poliomyelitis in a large city, carried out in 1972-1981, are presented. Two periods differing in morbidity rate, in the level of population immunity to poliomyelitis and in the activity of the poliovirus circulation are defined. The supervision of poliomyelitis is shown to be capable of influencing the course of the epidemic process of this infection provided that the individual elements of such supervision are correctly evaluated in different epidemic situations.     

Prevention and control of HIV infection in the Osh region of the Kyrgyz Republic

A total of 178 cases of HIV infection were diagnosed in the Osh region of the Kyrgyz Republic for January 1, 2003, the intensity of the prevalence of HIV infection being 14.5 per 100,000 of the population with this figure for the whole republic being equal to 5.9. In the dynamics of the HIV infection epidemic two periods were detected. During the first 3 years (1998-2000) a few individual imported cases of HIV infection were registered in the region. During the last 2 years (2001-2002) 98.8% of all cases of HIV infection registered in the region, as well as the presence of an epidemic outbreak among injection drug users (IDU), were detected. The risk factors of getting HIV infection were the intravenous use of drugs and a low level of information among young people concerning the routes of transmission of this infection and means of protection from HIV/AIDS: the promotion of healthy life style among young people, the introduction of the programs of "harm reduction" among IDU and the rules of safe sex.     

The manifestations of the epidemic process in shigellosis and their theoretical interpretation]

This work, based on the retrospective analysis of shigellosis morbidity among organized groups of adults, as well as the whole population of the city, demonstrates the manifestations of the epidemic process. Water supply was common in the city, while water consumption was autonomous. The organized groups of adults did not use the products of the local milk-processing factory. The following facts were established. The dynamics of morbidity in Flexner's dysentery showed the change of dominating variants of the infective agent, which reflected the action of internal mechanisms of the development of the epidemic process. The role of Sonne dysentery in the total structure of shigellosis morbidity did not correlate with the consumption of milk and milk products. The theory of the self-regulation of the parasitic system and the theory of correspondence served as the basis for the theoretical interpretation of the manifestations of the epidemic process of Shigella infections. To ascertain the real correspondence of individual Shigella species to concrete transmission factors, further investigation are necessary.     

The vaccinal prophylaxis of hepatitis B in Russia--the achievements, problems and outlook

Certain specific features of the present epidemic situation with hepatitis B (HB) in Russia were established: significant growth of HB morbidity, starting from 1995; the prevalence of persons aged 15-29 years among HB patients, which was linked with the sharp activation of the sexual route of the transmission of HB virus in recent years; an essential increase in the number of patients having contacted this virus in the process of the intravenous use of drugs. The results of the use of vaccine "Engerix B" among persons belonging to different risk groups were considered (a decrease in HB morbidity among them by 8-19 times was noted), the study demonstrated high immunogenicity anti-HBs antibodies on protective titers were determined in 92.3-95.7% of the vaccinees) and low reactogenicity of the vaccine, as well as stable postvaccinal immunity (5 years after the course of vaccination was completed anti-HBs antibodies were retained in 70.6-74% of the vaccinees). The study showed that only the vaccination of adolescents in combination, in the presence of opportunity, with the immunization of newborn infants and young children in the first year of their life made it possible to produce an essential effect on the activity of the epidemic process. Already in 2 years such organization of work on the prophylaxis of HB in one of the cities of the Sverdlovsk region led to a decrease in HB morbidity by 2.9 times, and among adolescents 9 times.     

Inter- and Intra-Host Viral Diversity in a Large Seasonal DENV2 Outbreak

Background

High genetic diversity at both inter- and intra-host level are hallmarks of RNA viruses due to the error-prone nature of their genome replication. Several groups have evaluated the extent of viral variability using different RNA virus deep sequencing methods. Although much of this effort has been dedicated to pathogens that cause chronic infections in humans, few studies investigated arthropod-borne, acute viral infections.

Methods and Principal Findings

We deep sequenced the complete genome of ten DENV2 isolates from representative classical and severe cases sampled in a large outbreak in Brazil using two different approaches. Analysis of the consensus genomes confirmed the larger extent of the 2010 epidemic in comparison to a previous epidemic caused by the same viruses in another city two years before (genetic distance = 0.002 and 0.0008 respectively). Analysis of viral populations within the host revealed a high level of conservation. After excluding homopolymer regions of 454/Roche generated sequences, we found 10 to 44 variable sites per genome population at a frequency of >1%, resulting in very low intra-host genetic diversity. While up to 60% of all variable sites at intra-host level were non-synonymous changes, only 10% of inter-host variability resulted from non-synonymous mutations, indicative of purifying selection at the population level.

Conclusions and Significance

Despite the error-prone nature of RNA-dependent RNA-polymerase, dengue viruses maintain low levels of intra-host variability.     

An "epidemic" model of sexual intercourse prevalences for black and white adolescents

In adolescence (12-16 years), the prevalence of sexual intercourse increases each year. To explain the increasing yearly prevalences, we propose a recursive equation model of onset of adolescent sexual intercourse. The model allows for an "epidemic" process (the transmission of sexuality from a nonvirgin to a virgin) and a nonepidemic process (two virgins progressing to sexual intercourse). The model also requires that virgin females be pubertally mature before they will progress to sexual intercourse. Adequate fits were obtained to the intercourse prevalences for both black and white respondents. Comparisons of alternative models established that the full model was superior to models that omitted either the nonepidemic process or the requirement of females' pubertal maturation. The model was able to fit both white and blacks simultaneously, assuming equal transition probabilities in both races. Hence, we propose the hypothesis that race differences in sexual intercourse prevalence may be strongly influenced by the age of initiation of the "epidemic" process and by race difference in females' rates of pubertal maturation. The results suggested that most new cases of sexual intercourse arose from the epidemic process and that males were more prone to progress to intercourse, given an opportunity.     

"They See Us as Resource": The Role of a Community-Based Youth Center in Supporting the Academic Lives of Low-Income Chinese American Youth

Based on a 15-week ethnographic-based research, this article examines the role of a community-based youth center in supporting the academic lives of Chinese American youth from low-income families in an east coast city I call "Harborview." This study demonstrates the significant role that community-based organizations play for low-income immigrant youth in providing them with social capital. This study also challenges the portrayal of Asian Americans as model minorities who do not face any barriers.  [Asian American education, community-based organizations, out-of-school-time programs, social capital]     

Adolescents’ Use of Care for Behavioral and Emotional Problems: Types,Trends, and Determinants

Objective

While adolescents use various types of care for behavioral and emotional problems, evidence on age trends and determinants per type is scarce. We aimed to assess use of care by adolescents because of behavioral and emotional problems, overall and by type, and its determinants, for ages 10–19 years.

Methods

We obtained longitudinal data on 2,230 adolescents during ages 10–19 from four measurements regarding use of general care and specialized care (youth social care and mental healthcare) in the preceding 6 months, the Child Behavior Checklist (CBCL) and Youth Self-Report, and child and family characteristics. We analyzed data by multilevel logistic regression.

Results

Overall rates of use increased from 20.1% at age 10/11 to 32.2% at age 19: general care was used most. At age 10/11 use was higher among boys, at age 19 among girls. Use of general care increased for both genders, whereas use of specialized care increased among girls but decreased among boys. This differential change was associated with CBCL externalizing and internalizing problems, school problems, family socioeconomic status, and parental divorce. Preceding CBCL problems predicted more use: most for mental health care and least for general care. Moreover, general care was used more frequently by low and medium socioeconomic status families, with odds ratios (95%-confidence intervals): 1.52 (1.23;1.88) and 1.40 (1.17;1.67); youth social care in case of parental divorce, 2.07 (1.36;3.17); and of special education, 2.66 (1.78;3.95); and mental healthcare in case of special education, 2.66 (1.60;4.51).

Discussion

Adolescents with behavioral and emotional problems use general care most frequently. Overall use increases with age. Determinants of use vary per type.     

The influence of concurrent partnerships on the dynamics of HIV/AIDS.

Most models of the spread of HIV/AIDS assume that the probability of transmission from an infected individual to a susceptible partner has some constant value per sexual act, compounding independently randomly (so that ten acts with one person chosen from a particular group has, on average, the same risk as one act with each of ten different people from that group). Guided by available data, other models treat the transmission process as being some characteristic (but highly variable) value per partnership, independent of the number of acts. This latter approach does not allow for the possible effects of concurrent partnerships, and therefore does not take account of the possibility that an initially uninfected partner of a given susceptible individual may become infected over the duration of their partnership. We present a new model, based on transmission per partnership, that takes account of partnership duration. If the number of overlapping partnerships is high enough (so that R0 greater than 1 among "standing crops" of partners), any initial infection will spread very fast--on the time scale of a few times the latent interval (a few months)--among existing networks of partners. After this initial "fast phase," the subsequent epidemic proceeds more slowly along conventional lines as new partnerships are formed. These properties of the model are illustrated numerically and by analytic studies (using singular perturbation theory). The possibility of such "two time-scale" phenomena could have implications for data analysis based on statistical back-projection.     

Some properties of a simple stochastic epidemic model of SIR type

We investigate the properties of a simple discrete time stochastic epidemic model. The model is Markovian of the SIR type in which the total population is constant and individuals meet a random number of other individuals at each time step. Individuals remain infectious for R time units, after which they become removed or immune. Individual transition probabilities from susceptible to diseased states are given in terms of the binomial distribution. An expression is given for the probability that any individuals beyond those initially infected become diseased. In the model with a finite recovery time R, simulations reveal large variability in both the total number of infected individuals and in the total duration of the epidemic, even when the variability in number of contacts per day is small. In the case of no recovery, R=infinity, a formal diffusion approximation is obtained for the number infected. The mean for the diffusion process can be approximated by a logistic which is more accurate for larger contact rates or faster developing epidemics. For finite R we then proceed mainly by simulation and investigate in the mean the effects of varying the parameters p (the probability of transmission), R, and the number of contacts per day per individual. A scale invariant property is noted for the size of an outbreak in relation to the total population size. Most notable are the existence of maxima in the duration of an epidemic as a function of R and the extremely large differences in the sizes of outbreaks which can occur for small changes in R. These findings have practical applications in controlling the size and duration of epidemics and hence reducing their human and economic costs.