Selection bias: neighbourhood controls and controls selected from those presenting to a Health Unit in a case control study of efficacy of BCG revaccination.

BACKGROUND: In most case control studies the hardest decision is the choice of the control group, as in the ideal control group the proportion exposed is the same as in the population that produced the cases. METHODS: A comparison of two control groups in a case control study of the efficacy of BCG revaccination. One group was selected from subjects presenting to the heath unit the case attended for routine prevention and care; the second group was selected from the neighbourhood of cases. All Health Units from which controls were selected offered BCG revaccination. Efficacy estimated in a randomized control trial of BCG revaccination was used to establish that the neighbourhood control group was the one that gave unbiased results. RESULTS: The proportion of controls with scars indicating BCG revaccination was higher among the control group selected from Health Unit attenders than among neighbourhood controls. This excess was not removed after control for social variables and history of exposure to tuberculosis, and appears to have resulted from the fact that people attending the Health Unit were more likely to have been revaccinated than neighbourhood controls, although we can not exclude an effect of other unmeasured variables. CONCLUSION: In this study, controls selected from people presenting to a Health Unit overrepresented exposure to BCG revaccination. Had the results from the HU attenders control group been accepted this would have resulted in overestimation of vaccine efficacy. When the exposure of interest is offered in a health facility, selection of controls from attenders at the facility may result in over representation of exposure in controls and selection bias.

Risk factors for treatment delay in pulmonary tuberculosis in Recife, Brazil.

BACKGROUND: Tuberculosis is still a great challenge to public health in Brazil and worldwide. Early detection followed by effective therapy is extremely important in controlling the disease. Recent studies have investigated reasons for delays in treatment, but there is no agreed definition of what constitutes an "acceptable" delay. This study investigates factors associated with total delay in treatment of tuberculosis. METHODS: A cohort of adult cases of pulmonary tuberculosis diagnosed over a two-year period was studied. Patients were interviewed on entry, reporting the duration of symptoms before the start of treatment, and sputum and blood samples were collected. It was decided that sixty days was an acceptable total delay. Associations were investigated using univariable and multivariable analysis and the population attributable fraction was estimated. RESULTS: Of 1105 patients, 62% had a delay of longer than 60 days. Age, sex, alcoholism and difficulty of access were not associated with delays, but associations were found in the case of unemployment, having given up smoking, having lost weight and being treated in two of the six health districts. The proportion attributable to: not being an ex-smoker was 31%; unemployment, 18%; weight loss, 12%, and going to the two worst health districts, 25%. CONCLUSION: In this urban area, delays seem to be related to unemployment and general attitudes towards health. Although they reflect the way health services are organized, delays are not associated with access to care.

Aleitamento materno e morbidade em crianças de 0 a 4 meses, das classes sócio-econômicas média e alta / Breastfeeding and morbity in infant from 0 to 4 months, in the middle and high socio-economic classes

O Aleitamento materno exclusivo é a forma ideal de alimentaçäo da criança até 6 meses de idade. As classes sociais mais elevadas no entanto relegam o valor tendo em vista as melhores condiçoes de higiene e o poder de compra dos alimentos além da maior participaçäo da mulher no mercado de trabalho. Pricura-se verificar a frequência de diarréia e infecçÖes respiratória em crianças de classes sócio-econômicas média e alta, de zero a 4 meses de idade, segundo o tipo de alimentaçäo - exclusivamente materna, mista e artificial. A pesquisa foi realizada em Clínica Pediátrica privada. Foram analisadas todas as fichas das crianças acompanhadas mensalmente, do nascimento até o 4§ mês de vida, num total de 162. As patologias consideradas foram diarréicas e infecçÖes do trato respiratório superior e inferior. No grupo de 0-2 meses de vida amamentadas exclusivamente, diarréia e/ou infecçoes respiratórias estiveram presentes em 2(6,5%), nas com alimentaçäo mista 9(19,6%) e naquelas alimentadas artificialmente 33(38,8%). Houve diferança significativa x*=p<13,86 (p<0.05). No grupo de 3 a 4 meses de vida, diarréia e/ou infecçÖes repiratórias estiveram presentes em 13(40,6%) das amamentaçoes exclusivamente com alimentaçäo mista e em 85 (65,4%) das alimentadas artificialmente. Diferença estatística significativa x*6,590,05. As crianças que receberam alimentaçäo materna exclusiva e mista apresentaram menor incidência de diarréia e infecçoes repiratórias demonstrando a importância do aleitamento materno também nestas classes sociais