PubMed Health⌕ Search

Biomedical subjects

J J Angulo

Publications and source records attributed to J J Angulo.

At least 19 recordsLinked to original sources
PubMed1987

Interdisciplinary approaches in epidemic studies--II: Four geographic models of the flow of contagious disease.

Straightforward adaptation of geographical and regional-science models to conceptual modeling of the epidemic spread of a contagious disease is achieved by: using analogies and isomorphisms, and using as a real example the observations made during a well studied epidemic of variola minor (the mild form of smallpox), a typical contagious disease. The adaptation of the Wilson model of planning for urban development includes a static view (network) of the structure and activities of the population and of organizations (diffusion agencies such as day schools), and the dynamic view (mechanism of epidemic spread) which includes the changes with time of elements of the network brough by flow of disease. Adaptation of the Brown model of spatial diffusion yields flows of disease occurring between micro-scale units (households) of social interactions but aggregations of these units do not participate explicitly in the flows. The occurrence of successive generations of affected households is specified as well as the occurrence of definite stages of the epidemic progression. Adaptation of the Alves-Morrill model of spatial diffusion yields a network of social groups and interdependencies; a simplified network of the mechanism of spread that shows flows of disease between individuals grouped into generations of infected individuals and generations of infective individuals; and a more realistic view which shows the flows of disease between real epidemiological units such as households and school classes. Adaptation of the Morrill-Manninen model of spatial diffusion concentrates on the mechanism and parameters having the epidemic spread as output. The interdependencies between the parameters and between each parameter and the epidemic spread are represented, including feedback processes. Brown's model seems to be the best for describing the epidemic spread of contagious disease while the Morrill-Manninen model is the most promising for investigating the detailed mechanism of the spread. Since these two models complement each other, their combined use is indicated.

Communicable Diseases↗
PubMed1984

An objective reconstruction of the chain of contagion.

North's clustering method, which is based on a much used ecological model, the nearest neighbor distance, was applied to the objective reconstruction of the chain of household-to-household transmission of variola minor (the mild form of smallpox). The discrete within-household outbreaks were considered as points which were ordered in a time sequence using a 10-40 day interval between introduction of the disease into a source household and a receptor household. The closer points in the plane were assumed to have a larger probability of being links of a chain of household-to-household spread of the disease. The five defining distances (Manhattan or city-block distance between presumptive source and receptor dwellings) were 100, 200, 300, 400 and 500 m. The subchain sets obtained with the five defining distances were compared with the subchains empirically reconstructed during the field study of the epidemic through direct investigation of personal contacts of the introductory cases with either introductory or subsequent cases from previously affected households. The criteria of fit of theoretical to empirical clusters were: (a) the number of clustered dwellings and of subchains , (b) number of dwellings in a subchain and (c) position of dwellings in a subchain . The defining distance closest to the empirical findings was 200 m, which fully agrees with the travelling habits of the study population. Less close but acceptable approximations were obtained with 100, 300, 400 and 500 m. The latter two distances gave identical results, as if a clustering ceiling had been reached. It seems that North's clustering model may be used for an objective reconstruction of the chain of contagious whose links are discrete within-household outbreaks.

Brazil↗
PubMed1983

Temporal-spatial-social parameters in the spread of contagious disease.

A conceptual theoretical model was built on the basis of prominent concepts of the generally accepted knowledge on the spread of contagious disease. Subsequently, the model was applied to a real epidemic of variola minor (the mild form of smallpox) and four phases of the epidemic were disclosed. The phases discriminated themselves through their relationships to invasion of certain city subdivisions and rural districts and particularly, through the type of social units involved and the type of persons introducing the disease into these units. Introduction of variola minor into day schools with further spread in classes passed across a threshold which led to a boosting of the number of households affected and of the area involved in the epidemic. The phase of maximal spread corresponded to this operation of day schools as diffusion agencies. The temporal-spatial-social correspondence suggests that phases of the epidemic did occur as a result of periodic variation of the mechanism of spread.

Brazil↗
PubMed1979

Variola minor in Braganca Paulista County, 1956: household aggregation of the disease and the influence of household size on the attack rate.

Household aggregation of cases, one possible characteristic of person-to-person transmitted disease, was formally tested in one epidemic of variola minor by using a pair statistic. A significant result was found for all households as well as for households grouped by the type of environment, or by the phase of the epidemic growth in time. Secondary attack rates, when related to household size (number of susceptibles) showed only a marginal trend in rural households but no trend in urban or semi-rural households.

Brazil↗
PubMed1977

Variola minor in Braganca Paulista county, 1956: a trend-surface analysis.

Trend-surface analysis (TSA), a form of polynomial regression used in geology, ecology and geography, was applied to analysis of the spread of an epidemic of variola minor in a small Brazilian city. Cubic surfaces gave a generalized map of the space-time distribution of the epidemic, allowing those parts of the city to be identified where variola minor was spreading rapidly or slowly. The epidemic spread relatively quickly over the core area of the city, especially to the peripherally located household dwellings in a northeast to south-west direction. The dwellings of adults and pre-school children introducing the disease into their households broadly followed the overall pattern. School child introductory cases from a southern-located school yielded a saddle-shaped contour pattern, centered about the school; but this pattern was not repeated for the school serving the northern half of the city, which showed a ridge-shaped pattern dipping toward the west. Cubic surfaces for the influence of certain household and individual characteristics were investigated, but showed only week trends. The nearest match to the bowl-shaped overall pattern of introductory dates was provided by the vaccination level of the households. From this application, it appears that TSA permits the identification of regional trends in an objective manner and gives a quantitative measure of the importance of these regional trends in terms of the overall variation in the spatial pattern.

Adult↗
PubMed1977

Analysis of the incidence of variola minor in an outbreak by use of a mathematical model.

The incidence of variola minor during an outbreak was analyzed by use of mathematical model B proposed by Chelsky and Angulo. Several parameters were estimated. Among these, the propagating rate (ratio of receptor cases to source cases) seems to predict the outbreak decline better than inspection of the incidence curve. The estimated mean generation interval (18.6 days) supports the thesis that variola minor is not transmitted at onset of illness but, on the average, about 4 days later. The ratio of clinical to subclinical infections (about 1 to 1) approximates those ratios found in serological surveys of variola minor and variola major outbreaks.

Brazil↗
PubMed1976

Variola minor in Bragança Paulista County, 1956: overall description of the epidemic and of its study.

An overall description of the epidemic of variola minor (alastrim) affecting Bragança Paulista County (Brazil) in 1956 is given. A total of 484 cases were recorded for 210 households, one hotel and one boarding school. At least 95 per cent of the households with cases of the disease in the capital city were surveyed and 90 per cent of the households in the rural districts. An orphanage, an old folk's home, the County jail and 10 schools operating in the capital city and some other social groups without cases were also surveyed, as well as 125 households without cases but with one or more contacts with the disease. An overall attack rate of 1924 cases, 267 cases and 781 cases per 100,000 inhabitants was obtained, respectively, for the capital city, the rural environment and the whole County. Clinical, epidemiological, serological and environmental surveys were conducted. Evidence on identification of the epidemic disease is presented. Study of the epidemic was made at these levels: the disease itself (frequency and severity); the disease in the individual (association of characteristics of persons with occurrence and clinical severity of variola minor); the disease in social units (occurrence and spread in households and school classes); the disease in small communities (occurrence and spread in housing projects, city blocks and farms); the disease in two large communities with contrasting socio-economic characteristics (the capital city and the rural environment); and the disease in the County as a whole.

Brazil↗
PubMed1976

Variola minor in Bragança Paulista county, 1956. Attack rates in various population units of the two schools including most students with the disease.

Overall attack rates were different for the two schools but were the same when only classes with cases were considered. Of the 49 classes (from both schools) with susceptible students, 29 had cases. In these, the attack rate among susceptibles ranged from 4-69%. The differences between the class rates were highly statistically significant. In the José Guilherme School, 17 out of 21 classes containing susceptibles had cases as compared with 12 out of 28 classes in the Jorge Tibiriçá School. Attack rates differed little between schools for either the early or late shift classes, but the attack rate for early shift classes in both schools together (39%) significantly exceeded that for the late shifts (16%). Within-shift attack rate differences were highly significant for the first-shift classes but not significant for classes in the other shifts. Attack rates differed significantly by classroom population (group of students using a classroom including all shifts), mainly because of heterogeneous rates in one school. Attack rates by desk column did not differ significantly even when comparing the column seating the earliest, the latest or the "previous" case in the class with the remaining columns. Attack rates by desk row also did not differ significantly. There was no important progressive association between attack rates and size of "unit of susceptibles" (group combining columns and rows), but there was a significant difference for unit size. Attack rates were not influenced by cluster seating of susceptibles.

Brazil↗
PubMed1976

Three tests for randomness of attack of social groups during an epidemic.

It is suggested that investigation of the attack of social units can be more illuminating of an epidemic process than the usual study of secondary attack rates of individuals. Three tests for detecting non-random differences in the occurrence of a disease between two groups of social units are presented. In each method the number of units attacked (X) in one of two groups of units is considered, rather than the number of individuals attacked. The tests are: (a) to use the Monte Carlo method, computer simulation of the epidemic process, to obtain an empirical distribution to which the observed value of X is compared; (b) to obtain the exact distribution of X; (c) to standardize X and compare it to the standard normal distribution. The three approaches are compared using data obtained from an epidemic of variola minor in two schools and the differences between the results are trivial. However, for large samples the only feasible approach is the Monte Carlo method.

Brazil↗
PubMed1975

Variola minor in Braganca Paulista County, 1956. Flow of the epidemic through the schools of the county.

The characteristics of the 10 elementary, teachers, business and high schools operated in the city capital of the Braganca Paulista County, state of São Paulo, Brazil, during the 1956 epidemic of variola minor (alastrim) are presented. Also shown are the numbers of students with variola and of students without variola but with homemates with variola, by grade and school. Of the total 131 cases recorded among students, 128 occurred in the 4 elementary schools. Of the latter cases, 101 occurred among the students of the JG School and the JT School. The distribution of these cases by age, sex, previous immunity status, school grade and clinical severity of the disease (typed according to Dixon's classification) were remarkably similar in these two schools. Only the ratio of students introducing the disease into their households to students having secondary cases in their households suggestively varied, the JT School having more introductory cases. No student with a previous attack of variola showed any clinical manifestation in any school. Only 2 of the total 101 cases from the JG and JT Schools occurred among students with a previous successful vaccination. Moreover, those two cases apparently resulted from within-household contacts rather than from contacts at the school. No student with current variola showed a severe type (Dixon's types 1 to 5). More than half of the cases typed showed the typical, medium-severity type (Dixon's type 6). More than 2/3 of the cases occurred among students aged 6 to 9 years, particularly among those 7- to 9-year old. The number of cases reached a maximum in the first grade and gradually and definitely decreased with increasing grade.

Adolescent↗
PubMed1974

Variola minor in Bragança Paulista County, 1956: lack of evidence indicating the influence of contaminated classrooms on spread of the disease.

Space-time interaction analysis was applied to data from 101 elementary school children who contracted variola minor during an epidemic in Bragança Paulista County, Brazil. One school had two and the other three shifts of students occupying the same classrooms each day. There was no evidence found for excessive numbers of cases to occur among unvaccinated students occupying the same desks or seated near the desks occupied by cases occurring during another shift. Only three cases occurred among the 31 unvaccinated students occupying desks of students with variola from other shifts. Only one of these three subsequent cases occurred at a time interval suggestive of transmission. For the three models tested there was no evidence of space-time interaction between time of onset of the disease and location of desk for pairs of students from different shifts.

Brazil↗
PubMed1974

On the use of contour maps in the analysis of spread of communicable disease.

The co-ordinates of the dwellings where cases of variola minor (alastrim) occurred during a small epidemic were used in a worked example of contour mapping of disease spread. The contoured variable was the date of onset, relative to an arbitrary base date, of the case introducing the disease into each of twenty-two households. Three contour maps prepared with slightly different computer programmes or dates exhibited similar concentric loops whose centres were close to the first infected household. The average rate of spread of the disease was estimated by regression of the number of days to onset of the first case in the household on the average distance from an arbitrary origin to the relevant contour line. The calculated average rate of spread was 1.22 metres per day. An additional map was contoured using the cumulative number of cases as the contoured variable, relative to the onset of the example epidemic.

Brazil↗