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Biomedical subjects

J S Koopman

Publications and source records attributed to J S Koopman.

At least 37 records · Page 2Linked to original sources
PubMed1994

Role of the primary infection in epidemics of HIV infection in gay cohorts.

A review of the data on infectivity per contact for transmission of the HIV suggests that the infectivity may be on the order of 0.1-0.3 per anal intercourse in the period of the initial infection, 10(-4) to 10(-3) in the long asymptomatic period, and 10(-3) to 10(-2) in the period leading into AIDS. The pattern of high contagiousness during the primary infection followed by a large drop in infectiousness may explain the pattern of epidemic spread seen in male homosexual cohorts in the early years of the epidemic. Simulations of cohorts of homosexual males, using that range of parameter values, indicate the following: (a) The initial fast rise and then more or less rapid flattening of the incidence curve of seropositives is primarily due to rapid initial spread, yielding a group of infecteds all of whom pass into the low infectivity asymptomatic period at close to the same time. All this occurs only if the basic reproduction number for the primary infection is > 1. (b) The behavioral changes that have been reported all started after the incidence of new infections began to fall, too late to have a major effect on the initial rise. The behavioral changes had a major effect in slowing down the subsequent rise in the number of seropositives. (c) High activity groups play an important role in the early rapid rise of the epidemic. However, it is not likely that the rapid decrease in rate of growth of seropositives is solely due to saturation of these very high activity groups. Although the evidence for this interpretation of the role of the primary infection is not conclusive, its implications for prevention and for vaccine trials are so markedly different from those of other interpretations that we consider it to be an important hypothesis for further testing.

Cohort Studies↗
PubMed1992

The link between sexually transmitted disease clinics and HIV counseling and testing centers: who is not getting referred?

A total of 236 clients attending human immunodeficiency virus (HIV) counseling and testing (C&T) centers and sexually transmitted disease (STD) clinics were interviewed to evaluate who is being reached by C&T services and if STD clients are being referred to HIV C&T centers. Respondents receiving HIV C&T reported significantly more sexual risk based on characteristics of their partners, whereas STD clinics respondents more frequently reported previous STD diagnoses and sex with prostitutes. Over 50% of the high-risk individuals attending STD clinics were not referred to HIV C&T centers. The differences in perceived risk of current and future infection between STD and HIV C&T centers and the low referral rates of high-risk individuals for HIV C&T indicate a need for increased education efforts, more effective risk-assessment policies in STD clinics, and a tightening of the link between STD clinics and HIV C&T centers.

Adolescent↗
PubMed1992

Protective effect of antibiotics on mortality risk from acute respiratory infections in Mexican children.

A case-control study of mortality from acute respiratory infections (ARI) among children under five years of age was conducted in Naucalpan, an urban-suburban area of Mexico City, and in rural localities of Tlaxcala, Mexico. The study found that ARI deaths tended to occur in the poorest neighborhoods; 78% of the deceased study subjects were infants under six months old; and 68% of the deaths occurred at home. Comparison of the data for cases (fatalities) and control children who had severe ARI but recovered showed that failure to receive antibiotics was associated with death (odds ratio 28.5, 95% confidence interval 2.1-393.4). This antibiotic effect was controlled for numerous potentially confounding factors. It is evident that antibiotics had a much greater effect in the early days of the illness than later on. In general, the findings strongly support PAHO/WHO primary health care strategies--including such strategies as standardized management of severe ARI cases--that seek to reduce childhood ARI mortality.

Anti-Bacterial Agents↗
PubMed1991

Assessing risk factors for transmission of infection.

Commonly used measures of effect, such as risk ratios and odds ratios, may be quite biased when used to assess the effect of factors that alter transmission risks given exposure to infected individuals. This is demonstrated in a simulation model involving a higher-risk behavior and a lower-risk behavior affecting the sexual transmission of human immunodeficiency virus. The bias arises because population contact patterns between higher-risk and lower-risk persons change their relative probabilities of exposure to an infected individual as an epidemic progresses. The assessment of contact patterns is thus central to risk assessment for contagious diseases. A new formulation of selective mixing presented here, together with a structured mixing specification of the social settings of contact, provides a theoretic framework for the investigation of contact pattern determinants.

Bias↗
PubMed1991

Determinants and predictors of dengue infection in Mexico.

A national serosurvey was conducted in Mexico from March to October 1986 to identify predictors of dengue transmission and target areas at high risk of severe annual epidemics. A total of 3,408 households in 70 localities with populations less than 50,000 were randomly sampled, and serology was obtained from one subject under age 25 years in each household. When comparing exposure and infection frequencies across the 70 communities, the authors found that median temperature during the rainy season was the strongest predictor of dengue infection, with an adjusted fourfold risk in the comparison of 30 degrees C with 17 degrees C. High temperatures increase vector efficiency by reducing the period of viral replication in mosquitoes. The proportion of houses in a community with larva on the premises was significantly associated with the community proportion infected (odds ratio (OR)adj = 1.9; 95% confidence interval (CI) 1.4-2.5), as was the proportion of households with uncovered water containers present (ORadj = 1.9; 95% CI 1.4-2.7). Because these factors have effects beyond the individual household and subjects infected from them create a risk for other subjects, both analyses of effects and organization of control efforts must be at the community level. A predictive model was constructed using the community level risk factors to classify communities as being at high, medium, or low risk of experiencing an epidemic; 57% of these communities were correctly classified using this model.

Adult↗
PubMed1991

Medical student attitudes toward the treatment of HIV-infected patients.

The intention to treat HIV-infected persons and correlates of those intentions were examined in a cross-sectional sample of 1st- and 2nd-year medical students (n = 201). An anonymous questionnaire measured knowledge of HIV transmission, intention to provide medical care to HIV-infected persons, comfort in performing a physical examination on patients from subgroups with high HIV prevalence, level of homophobia, professional altruism, and personal perceived risk of HIV infection. Intention to provide medical care was considered as the dependent variable. All variables except perceived personal risk were found to be significantly related to the intention to provide medical care although knowledge showed the weakest relationship (Odds Ratio = 2.14). The presence of professional altruism and the presence of homophobia were associated with a significant increase in the effect of knowledge on increasing the intention to treat. Results of this report support other studies that showed that factors other than knowledge play a role in clinical decision making regarding patients with AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Epigenesis theory: a mathematical model relating causal concepts of pathogenesis in individuals to disease patterns in populations.

A mathematical modeling approach called epigenesis theory is presented which relates three aspects of pathogenesis to the population distribution of disease. The three aspects of pathogenesis involve how two or more measured variables interact. They are 1) whether the measured variables are related to the same causal action, 2) whether there is only one pathogenic process leading to disease, and 3) whether the measured variables contribute to the same pathogenic process. Epigenesis theory defines the following multivariable relations between two disease causes: 1) "Complementary" causes contribute different causal actions to the sole pathogenic process leading to disease. They have multiplicative relations. 2) "Separate process" causes contribute different causal actions to different pathogenic processes. They have the relations of simple independent action which are slightly less than additive. 3) "Intermediate" causes contribute different causal actions to the same pathogenic process in the presence of additional pathogenic processes where at most one of them may also participate. They have relations somewhere between multiplicative and simple independent actions. 4) "Cooperative-competitive" causes share the same causal action and act within the same pathogenic process. Their relations can change from greater than multiplicative to less than simple independent action at increasing dichotomization points of the measured variables. Epigenesis theory unifies the sufficient-component causes model and the simple independent action model and exceeds either model in the range of observations it can explain. It is most useful given directly causal measured variables and specific disease outcomes, but it will assist in etiologic investigations of nonspecific outcomes in which new disease classifications are proposed. While it is less useful given surveillance-type variables such as age or sex or outcomes resulting from numerous pathogenic processes such as death, it gains utility as more causal variables are entered into an analysis and as more cut points of continuous complementary, independent, or intermediate variables are distinguished.

Adult↗
PubMed1990

Behavioral change in longitudinal studies: adoption of condom use by homosexual/bisexual men.

We compared reporting serial cross-sectional prevalence of sexual behavior over time, to reporting individual patterns of behavioral change in a cohort of homosexual men at a six-month interval. Aggregate prevalence rates underestimated the magnitude of change to safer practices, and failed to provide information on relapse to less safe practices. We conclude that it is important to report data based on individual fluctuations in behavior for the evaluation of change over time.

Adult↗
PubMed1989

The Tecumseh Study. XV: Rotavirus infection and pathogenicity.

Rotavirus infection and associated symptoms were studied prospectively from 1976 through 1981 in a 10% sample of families in Tecumseh, Michigan. Infection was determined using an antibody enzyme-linked immunosorbent assay (ELISA) method designed for use with large numbers of sera collected semiannually. Illness was identified from symptoms ascertained weekly by telephone. Risks of infection during a rotavirus season varied from 4.8% in 1978 to 9.2% in 1980. Risks were 20.6% in the under two years age group and decreased progressively with age to 3.6% in individuals aged 45 years or over. Preschool children accounted for less than 20% of the infections in the population of reference. Infection was associated with diarrhea in the first two years of life and with both diarrhea and vomiting later in life. There was no evidence for association of rotavirus infection with a gastrointestinal-respiratory syndrome. The pathogenicity of infection, the protectiveness of antibody, and the socioeconomic correlates of infection showed marked changes from year to year. In 1978, there was a dramatically higher pathogenicity and a greater protectiveness of ELISA measured antibody than in other years. There was also a dramatic reversal in the socioeconomic relations of infection from 1977 to 1978. Taken together, these findings suggest that different rotaviruses might have predominated in these years.

Adolescent↗
PubMed1989

The Tecumseh Study. XVI: Family and community sources of rotavirus infection.

The effect of age on transmission of rotavirus infection within households and on the risk of infection from outside of the household was investigated through analyses of serum pairs. These paired specimens had been collected from individuals of all ages in families of diverse age composition in Tecumseh, Michigan. Serologic observations on 1,508 individuals divided into 0-1, 2-4, 5-9, 10-17, and 18+ year age groups provided infection determinations on 3,311 person-seasons during the 1977 through 1981 rotavirus seasons. Infection occurring in an individual in each age group was generally associated with infection in all other age groups in the household. Despite these associations by household, two different means of estimating the proportion of all infections acquired in the household yielded estimates of only 17 and 20%, indicating the importance of community acquisition of infection. Very young children had a very small percentage of their infections acquired in the household, while progressively older ages had an increasing percentage of infections acquired there. These results indicate that a strategy of indirectly protecting infants from infection by preventing infection in their household contacts would be inefficient.

Adolescent↗
PubMed1988

Dengue epidemics on the Pacific Coast of Mexico.

Dengue epidemics in three Mexican cities were investigated with retrospective surveys and virus isolations from acute cases. These epidemics were part of the continuing extension of dengue in Mexico since 1978 after 15 years without transmission. Serotype 1 dengue infection predominated in all epidemics, but in one city, type 2 strains were also isolated. The following findings were consistent in all three cities: 1) illness history provided evidence of presence of infection months before the epidemic became evident, 2) there was a very sharp and progressive increase of dengue illness attack rates by age, 3) there were no interpretable relationships between illness and the presence of different types of breeding sights in the home, 4) socioeconomic status was strongly negatively related to illness, and 5) geographical factors not related to the other measured variables had a strong effect on illness rates reflecting the focality of transmission. In addition, there was evidence of a strong protective effect against illness by the use of mosquito netting or the presence of screens on houses, but these relationships were not universal to all three cities.

Adolescent↗
PubMed1988

Statistical inference for infectious diseases. Risk-specific household and community transmission parameters.

A statistical model is presented for the analysis of infectious disease data from family studies in the community. The model partitions the sources of infection into those from within the household and those from the community at large. The parameters reflecting these sources of infection are estimated as functions of the risk factors. This new model is used to overcome problems associated with the lack of independence of observations in infectious disease data and negative confounding due to the association of unmeasured exposures and immunity. An example of how this new statistical model is used to provide a clearer and less confounded description of risk factor effects is presented for data from influenza A(H3N2) epidemic seasons in the Tecumseh Respiratory Illness Study. The risk factors examined are age and pre-epidemic season antibody level as measured by the hemagglutination-inhibition test, while the outcome is the infection rate. A standard analysis of the data indicates that the efficacy of protective antibodies is 70% in children and only 47% in adults. However, such an efficacy measurement is negatively confounded by past exposure which is age dependent. By means of the model, the true, unconfounded, efficacy of protective antibodies is shown to be 90% in both adults and children.

Adolescent↗
PubMed1986

The Tecumseh Study of Illness. XIV. Occurrence of respiratory viruses, 1976-1981.

During 1976-1981, surveillance of respiratory infection in Tecumseh, Michigan included isolation of respiratory viruses using methods similar to those employed in 1965-1971. As in the earlier period, influenza viruses continued to be isolated annually, but not without some changes in regularity of appearance. Parainfluenzaviruses also exhibited some marked changes in patterns of occurrence, but years of activity of parainfluenza types 1 and 2 were similar to those reported in other studies. Respiratory syncytial viruses continued to be limited in appearance to relatively brief periods. Rates of isolation of parainfluenzaviruses and respiratory syncytial viruses demonstrated their importance in reinfections of older children and adults. This was confirmed by examination of characteristics of associated illnesses.

Adolescent↗
PubMed1985

Analyzing the joint effects of two antibodies and the design of molecularly engineered vaccines.

A new analytical approach to determine how antibodies relate to each other in producing immunity is presented. One purpose of this analysis is to decide on the antigenic composition of vaccines. Regression analyses and single discrete analyses are shown to be inappropriate to this task. The proposed analyses makes multiple cut points on two pre-exposure antibody levels. At each resulting discrete classification, additive and multiplicative interaction parameters are calculated. Various models of joint antibody action are shown to produce two general patterns of interaction terms with this type of analysis. One pattern characterizes situations where each antibody, or something substituting for the action of each antibody, is always needed to eliminate all infections. This may be because the antigens to which the antibodies are directed are on separate microbes or because microbes can only be neutralized by the joint action of both antibodies. A second pattern characterizes situations where both antibodies act cooperatively but given high enough levels only one may be needed. This may be because the antibodies have the same molecular effect or because they act by separate means against the same organisms in an innoculum.

Antibodies↗
PubMed1985

Tecumseh study of illness. XIII. Influenza infection and disease, 1976-1981.

The occurrence of influenza was followed in Tecumseh, Michigan during the five year period 1976-1981 by identifying onset of acute respiratory illness and by virus isolation and serology. Type B outbreaks were observed in 1976-1977 and 1979-1980, type A (H3N2) in 1977-1978 and 1980-1981, and type A (H1N1) viruses in 1977-1978, 1978-1979, and 1980-1981. Evidence of low level circulation of viruses in the year preceding an outbreak was not obtained. Age-specific isolation rates from specimens collected by the community physicians differed from age-specific isolation rates from specimens collected from the surveillance, suggesting the operation of a selection mechanism in the former. Symptoms associated with virus isolation were strongly influenced by age. Within age groups, several variables, especially median duration, indicated type A (H3N2) had produced the most severe illnesses, type A (H1N1) the mildest, with type B intermediate. Age-specific infection rates determined by serology for the 1976-1977 and 1977-1978 influenza seasons confirmed the consistently high rates for type A (H3N2) in children with some fall-off with increasing age. Type A (H1N1) rates peaked in children aged 5-19 years and type B in children aged 5-14 years. This may be related in part to insensitivity of the hemagglutination inhibition test in those under age 5 years. Infection with type A (H1N1) was detected at low frequency in adults. Pathogenicity was calculated based on the serologic data. It was estimated for all ages combined that, at a minimum, type A (H3N2) infection produced febrile illness in 25% of cases and type B infection produced respiratory illness in 34% of cases.

Adolescent↗
PubMed1985

Infant formulas and gastrointestinal illness.

Infants under age one in a pediatric practice were followed prospectively, and the determinants of acute gastrointestinal illness were evaluated in case-control pairs, matched by birth month. The risk of acute gastrointestinal illness in infants receiving formula was six times greater than in infants receiving breast milk and 2.5 times greater than in infants receiving cow milk. In the second six months of life, infants on formula had 0.38 more gastrointestinal illness episodes per child than infants on cow milk. Episodes without rotavirus or bacterial agents accounted for most of the increased risk of formula. The increased risk could not be explained by iron fortification of the formulas, prescription of non-milk based formulas to high-risk infants, case ascertainment bias, control selection bias, or numerous control factors. Non-antibody anti-infection properties found in cow milk are one possible explanation for these findings.

Animals↗