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I M Longini

Publications and source records attributed to I M Longini.

At least 55 records · Page 3Linked to original sources
PubMed1991

A generalized stochastic model for the analysis of infectious disease final size data.

A stochastic infectious disease model was developed by Ball (1986, Advances in Applied Probability 18, 289-310) in which the distribution of the length of the infectious period is allowed to have any distribution that can be described by its Laplace transform. We extend this model such that the infection can be transmitted within the population or from an unspecified source outside the population. Also, discrete heterogeneity in the population can be modeled to incorporate variable susceptibility, variable infectivity, and/or mixing behaviors. The model is fitted to serologic data from two influenza epidemics in Tecumseh, Michigan, using maximum likelihood estimation procedures. The estimates show a clustering pattern by age groups.

Adult↗
PubMed1990

Estimating benefits of screening from observational cohort studies.

Analysis and interpretation of observational studies of screening effectiveness is difficult because several biases threaten validity, including the structural healthy screenee bias, length bias, and effects of lead time. Although methods for the analysis of observational studies of screening effectiveness have been proposed, most have limitations such as incomplete control of length bias, or a heavy reliance on distributional assumptions. In this report we present a method for the analysis of observational cohort studies of screening effectiveness. Although developed independently and formulated specifically for estimating benefits of screening, our approach is implied by a more general approach developed previously by Robins. Our approach, in contrast to other available methods, avoids the healthy screenee bias, and length and lead time bias, and allows an empirical approach to analysis that need not depend highly on distributional assumptions. We illustrate application of the approach with analysis of published data from a study of breast cancer screening.

Bias↗
PubMed1990

Simulation of mechanisms of viral interference in influenza.

Biological interference among viral agents might have significant implications for disease prevention and therapy. Field data for influenza yield conflicting evidence concerning the independence of infection rates, or disease severity, for two co-circulating viruses. To examine the effects of several assumed modes of interference for influenza, simulations of a Monte Carlo micropopulation model of influenza epidemics have been performed. Model parameters were selected so that the simulated attack rates for each of two different viral strains matched actual field data. Rates of infection were compared for single agents and for two viruses with only behavioural interference. Other simulations included temporary immunity to the other virus for the duration of the infection, and/or reduced shedding of viral particles for dual infections. Simulated viral competition had little impact on epidemic severity, duration, or size distribution. Under the conditions studied, viral interference in natural populations would be difficult to infer from field observations of attack rates. Other simulations extended a partial immunity and/or reduced viral shedding during an infection with a second virus. These indicated that interference might be suggested by field data, but it could not be demonstrated conclusively. Still other simulations showed that for epidemics with much higher attack rates for both viruses, it would be relatively easy to demonstrate interference. However, in order to observe interference between influenza strains, it would be necessary to monitor on an almost daily basis, using a method of viral detection which would have to be both highly specific and also very sensitive.

Adolescent↗
PubMed1990

[Direct and indirect effects of vaccines: an annotation on the estimation of the vaccine efficacy from outbreaks caused by acute infection agents such as measles].

A good measure of the efficacy of vaccines should be based on an index that standardizes the exposure to infection of those who have been immunized and those who have not. In addition, the measure should not be influenced by indirect effects. In the case of outbreaks directly transmitted agents that cause acute infections diseases, the household secondary rates of attack are the best indicator of vaccine efficacy provided that the data are collected at the household level. If the data are not collected in this manner, the best indicator will be the estimated probability of transmission, even though this estimator and its meaning less obvious than the secondary attack of rate. Other strategies to estimate the efficacy of an immunization are more appropriate for situations that are more complex than outbreaks caused by acute infectious agents.

Antibodies, Viral↗
PubMed1989

Duration of human immunodeficiency virus infection before detection of antibody.

To estimate the duration and frequency of the period of HIV infection without detectable antibody, modelling techniques were applied to results of detection of HIV DNA by means of the polymerase chain reaction (PCR) and to data from cases in published reports. PCR was carried out with gag and env region primers on samples from 27 homosexual and 12 haemophilic men for whom stored samples were available from before and after seroconversion; serum was also tested for p24 antigen by antigen-capture enzyme immunoassay. HIV DNA was detectable before seroconversion in 4 men; in all 4 PCR was positive only in the seronegative sample taken closest to the time of seroconversion. In 3 men antigen was detected before seroconversion; in each case HIV DNA was also detected. By a Markov model, the time from infection with HIV (as assessed by detection of HIV DNA) to first detection of HIV antibody was estimated to be 2.4 (SE 2.1) months for the median individual. Modelling of cases of HIV infection with known exposure in published reports gave a median estimate of 2.1 (0.1) months from exposure to antibody detection, and 95% of cases would be expected to seroconvert within 5.8 (0.6) months. HIV infection for longer than 6 months without detectable antibody seems uncommon.

Acquired Immunodeficiency Syndrome↗
PubMed1989

Statistical analysis of the stages of HIV infection using a Markov model.

We use a staged Markov model to estimate the distribution and mean length of the incubation period for acquired immunodeficiency syndrome (AIDS) from a cohort of 603 human immunodeficiency virus (HIV) infected individuals who have been followed through various stages of infection. The model partitions the infected period into four progressive stages: (1) infected but antibody-negative; (2) antibody-positive but asymptomatic; (3) pre-AIDS symptoms and/or abnormal haematologic indicator; and (4) clinical AIDS. We also model a fifth stage: death due to AIDS. The estimated mean (median) waiting times in each stage of infection are stage 1, 2.2 (1.5) months; stage 2, 52.6 (36.5) months; stage 3, 62.9 (43.6) months; and stage 4, 23.6(16.3) months. We estimate the mean AIDS incubation period (from infection to development of clinical AIDS) as 9.8 years with a 95 per cent confidence interval of [8.4, 11.2] years. The paper also considers the estimated density function of the AIDS incubation period and the estimated survival functions for individuals in each stage of infection. This work represents one of the most complete statistical descriptions to date of the natural history of HIV infection.

Acquired Immunodeficiency Syndrome↗
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

Efficacy of virucidal nasal tissues in interrupting familial transmission of respiratory agents. A field trial in Tecumseh, Michigan.

A randomized field trial was conducted in Tecumseh, Michigan, to test the efficacy of virucidal nasal tissues in interrupting transmission of respiratory agents in the household. In the double-blinded trial, 296 households were stratified by household size and randomly assigned to the group using treated tissues and the group using placebo tissues. Households were recruited in late August to early September 1984, and the tissues were distributed in November 1984. A 10-week influenza A(H3N2) period was identified from January 13 to March 23, 1985, although there was also evidence of rhinovirus circulation during that period. A household-level infection transmission model was used to assess the effectiveness of the virucidal tissue in the household. The model was used to estimate the secondary attack rate for the placebo and treated tissue households during the influenza A(H3N2) period. The efficacy of the treated tissue in interrupting secondary transmission was found to vary from 30.1% to 36.9%, although it could be as high as 39.4% when historical comparisons are used. However, these differences were not statistically significant. In general, the use of virucidal nasal tissue in the household appears to result in the partial interruption of transmission of influenzavirus from an infected household member to another household member during an influenza epidemic.

Adult↗
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↗
PubMed1988

Models for the statistical analysis of infectious disease data.

The Longini-Koopman model (1982, Biometrics 38, 115-126) describes the process underlying the transmission of an infectious disease in terms of household and community level transmission probabilities. This model is generalized by allowing for different transmission probabilities that may correspond to various levels of risk factors on both the household and community levels. Two types of models are considered: (i) models for household data, where the numbers of susceptible and infected members in each household are known along with the values of household level risk factors; and (ii) models for individual data, where the infection status and risk factor level are known for each individual in the household. Although the type (i) models can be expressed as special cases of the type (ii) models, they deserve special attention as they can be represented and analyzed as log-linear models. Both types of models can be analyzed using maximum likelihood methods, while the type (i) models, when expressed as log-linear models, can also be analyzed by the weighted least squares method. Data from influenza epidemics in Tecumseh, Michigan and Seattle, Washington are used to illustrate these methods.

Adult↗
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↗
PubMed1984

Statistical procedures for estimating the community probability of illness in family studies: rhinovirus and influenza.

A statistical method is presented for determining acquisition rates of illness from community sources of infection and for distinguishing among viruses which are associated with different epidemic seasons. The new method consists of a computationally simple procedure for estimating the community transmission parameter and the standard error of the estimator. This method, as well as a previously developed maximum likelihood procedure, is applied to illness data as a means for distinguishing among broad patterns of illness acquisition. The periods evaluated are the rhinovirus, influenza A and influenza B seasons in Tecumseh, Michigan, for the years 1976-1980. Tecumseh households are stratified into exposure groups depending on age-group composition. Estimates are found for the risk differences of illness acquired from the community for households with different age-group distributions. Analysis of the Tecumseh data reveals that members of households with children are more apt than members of households without children to acquire illness associated with rhinovirus, influenza A and influenza B from the community. Members of households with just preschool children (and adults) are more apt than members of households with just school children (and adults) to acquire illness associated with rhinovirus and influenza B from the community. In contrast, members of households with just preschool children (and adults) are just as likely as members of households with just school children (and adults) to acquire illnesses associated with influenza A from the community.

Adolescent↗
PubMed1984

Simulation studies of influenza epidemics: assessment of parameter estimation and sensitivity.

The influenza simulation model of Elveback et al is used to evaluate the accuracy of the maximum likelihood procedure of Longini et al for estimating the secondary attack rate in households. The sample population from the Tecumseh Respiratory Illness Study is mapped into the simulation model and simulations are carried out over a range of parameter values and conditions, some of which were derived from influenza seasons in Tecumseh and from the Seattle Flu Study for the years 1975-1980. The estimation procedure is found to be quite robust for parameter values preset within appropriate limits for influenza. However, a significant difference is found between the preset and estimated household contact parameter for epidemics of medium and high intensity when the preset value is zero. Incremental increases in the household contact parameter are shown to produce marked increases in the overall infection attack rate demonstrating that household spread is an important link in maintaining infection in other mixing groups such as schools, preschool groups and neighbourhood clusters of households.

Adolescent↗
PubMed1984

Environmental and genetic sources of familial aggregation of blood pressure in Tecumseh, Michigan.

Environmental and genetic sources of variation in blood pressure have been assessed for an 82% sample of the Tecumseh, Michigan, population during the period 1962-1965. Correlations of systolic blood pressure and diastolic blood pressure were calculated for sets of related and unrelated individuals living together and related individuals living apart. These correlations were analyzed using a biologic model which partitions the total phenotypic variance into components associated with shared genes and components associated with shared household environments both within and across generations. Heritabilities were estimated to be 0.42 and 0.30 for systolic blood pressure and diastolic blood pressure, respectively. The model confirms the hypothesis that the determinants of blood pressure consist of both significant genetic (p less than 0.005) and environmental (p less than 0.005) components. However, only the shared household environments within generations were found to be significant for systolic blood pressure (p less than 0.005) and diastolic blood pressure (p less than 0.05). Although not significant, the across generation shared environment between mothers and offspring tended to have some importance, while that between fathers and offspring was negligible. The implication that there may be some maternal influence in addition to the genetic influence on the determination of blood pressure in offspring warrants further investigation.

Adolescent↗