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.

Frequencia de anticorpos para rotavirus em habitantes da cidade de Sao Paulo em 1980-82. / Frequency of antibodies to rotavirus in inhabitants of the city of Sao Paulo in 1980-82

Entre maio de 1980 e julho de 1982 foram selecionadas ao acaso 1.202 amostras de sangue de individuos encaminhados do Instituto Adolfo Lutz. Usou-se o metodo da inibicao da hemaglutinacao, visando titular anticorpos para rotavirus. O antigeno usado foi obtido da cepa de virus SA-11.Os resultados de 426 soros de criancas entre 0-23 meses de idade indicam que a distribuicao da infeccao e semelhante aquela encontrada em outros paises. Diminuicao dos anticorpos maternos ocorreu aos 6-7 meses de idade e o pico da frequencia ocorreu nos 1o. e 2o. anos de vida. Em seguida nao houve variacoes de interesse inclusive ate a faixa igual ou maior de 70 anos sugerindo reinfeccoes no decorrer da vida. Estatisticamente, os resultados em 738 amostras de soros entre 2-59 anos nao diferiram significantemente dos obtidos pelo metodo ELISA em outros paises, razao pela qual o metodo, alem de menos oneroso, e mais simples e deve ser usado em inqueritos sorologicos e estudos retrospectivos de surtos e/ou epidemias da infeccao

Contour mapping of the temporal-spatial progression of a contagious disease.

A methodology for contour-map study of contagious-disease epidemics is presented. Its application is exemplified in a smallpox epidemic occurring in a small Brazilian town. Computer-controlled contour-mapping of dates of introduction of variola minor into 169 households and the coordinates of the affected dwellings did not show a single contour pattern, but a group of subareal patterns of within-household outbreaks. Introduction by adults and pre-school children were distributed throughout the whole city area. However, introduction by school children formed two groups of contours and of affected dwellings. Each group was included in a discrete area corresponding to the zone of pupil recruitment of the two schools enrolling 91% of the school-child introductory-cases. The latter were responsible for introduction of the disease into 45% of the city's affected households. Altogether, both zones practically covered the whole city area. In either zone, several patterns surrounded the corresponding school. Even though no time value was entered for any school, contour maps clearly evidenced the influence of those two schools on spread of the epidemic. An estimated rate of linear spread of variola minor was 1.35 m per day in a city subarea.

Variola minor in Bragança Paulista County, 1956. Distribution of onset of cases in the two schools including most school children with variola.

Class attendance during illness was confirmed for numerous pupils of two schools. Successive generations whose median cases were separated by an interval consistent with the "serial interval" of variola minor were clearly found in the epidemic curve for II of the 29 classes with cases from both schools. Twenty two other classes had no case at all.

Variola minor in Bragança Paulista County, 1956. Respiratory manifestations in cases of variola and in household contacts of cases.

A respiratory complication was recorded for 62 of the 485 cases of variola minor occurring in Bragança Paulista County, Brazil, 1956. The respiratory complication preceded onset of the classical variola minor in 2 cases; lasted only the pre-eruptive phase in 38 cases; lasted only the eruptive phase in 9 cases; lasted both the pre-eruptive phases in 1 case and had an unrecorded relationship to the clinical course in 12 cases. Six of the 17 household contacts with a respiratory syndrome contemporaneous with variola in the household had previously suffered from variola.