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

Vacina BCG contra tuberculose: efeito protetor e políticas de vacinação

OBJECTIVE: The BCG vaccine has been in use since 1921, but still arouses controversy and uncertainties. The objective was to analyze the protective effect of the BCG vaccine in its first and second doses and the accompanying vaccination policies. METHODS: A systematic review of the literature in both English and Spanish was carried out, covering the period 1948 to 2006, using the PubMed database. The main search terms used included BCG vaccine, BCG efficacy, BCG and tuberculosis. The studies were grouped by design, with the main results from the clinic tests, case-control studies and meta-analyses presented separately. RESULTS: The protective effect of the first dose of the BCG vaccine against tuberculosis in its miliary and meningeal forms is high. However, the results vary in relation to the pulmonary form of the disease, with some indicating zero effect and others levels of nearly 80%. Research is being carried out to develop new vaccines that could substitute the BCG or be used as a booster. CONCLUSIONS: There are evidences that the protective effect of the BCG vaccine does not increase with a second dose. In spite of its limitations and the expectation that a new tuberculosis vaccine will be developed in the future, the BCG vaccine remains an important tool in controlling the harmful effects of tuberculosis, particularly in countries with medium or high incidence levels of the disease.OBJETIVO: A vacina BCG é utilizada desde 1921, embora ainda apresente controvérsias e aspectos não esclarecidos. O objetivo do artigo foi analisar aspectos relacionados ao efeito protetor da primeira e segunda doses da vacina BCG e as políticas de vacinação adotadas. MÉTODOS: Foi realizada revisão sistemática da literatura publicada em inglês e espanhol, abrangendo o período compreendido entre 1948 e 2006, na base PubMed. Os principais descritores utilizados foram BCG vaccine, BCG efficacy, BCG e tuberculosis. Os estudos foram agrupados por tipo de desenho, apresentando-se separadamente os principais resultados de ensaios clínicos, estudos de caso-controle e metanálises. RESULTADOS: O efeito protetor da primeira dose da vacina BCG contra a tuberculose na forma miliar ou na meningite é elevado. No entanto, os resultados são discordantes em relação à forma pulmonar, variando de ausência de efeito a níveis próximos a 80%. Estão sendo conduzidas pesquisas sobre novas vacinas candidatas a substituir a BCG ou serem utilizadas como reforço. CONCLUSÕES: Há evidências de que a segunda dose da BCG não aumenta o seu efeito protetor. Apesar de seus limites e da expectativa futura de nova vacina para tuberculose, a vacina BCG mantém-se como importante instrumento no controle dos efeitos danosos da doença, sobretudo em países com taxas de incidência médias e elevadas

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

Avaliação da efetividade da segunda dose da vacina BCG contra tuberculose em crianças e adolescentes na Região Metropolitana de Recife

A vacina BCG (bacilo de Calmette e Guerin), única e mais antiga usada mundialmente para controle da tuberculose, tem sua história cheia de controvérsias e dúvidas sobre sua eficácia ou efetividade. Utilizada pela primeira vez em 1921 como uma grande esperança para controlar uma doença que dizimava populações sem que se tivesse poder de controle sobre a mesma, veio posteriormente sofrer uma grande perda de credibilidade, com o acidente de Lübeck em 1930, na Alemanha, onde um grande número de crianças morreu após terem recebido a vacina BCG. Acidente depois esclarecido, quando descoberto que foi utilizado na preparação da vacina não o bacilo atenuado de Calmette e Guèrin, mas uma cepa virulenta do bacilo de Köch. A autora se propõe nesse artigo fazer uma breve reflexão sobre a vacina BCG, as controvérsias sobre sua efetividade e ou eficácia, descrita nos vários desenhos de estudo realizados no Brasil e no mundo, sem pretensão de esgotar o assunto e sobre as novas vacinas que vêm sendo avaliadas ainda em fase experimenta

Factors associated with treatment failure, dropout, and death in a cohort of tuberculosis patients in Recife, Pernambuco State, Brazil.

A cohort of cases initiating tuberculosis treatment from May 2001 to July 2003 was followed in Recife, Pernambuco State, Brazil, to investigate biological, clinical, social, lifestyle, and healthcare access factors associated with three negative tuberculosis treatment outcomes (treatment failure, dropout, and death) separately and as a group. Treatment failure was associated with treatment delay, illiteracy, and alcohol consumption. Factors associated with dropout were age, prior TB treatment, and illiteracy. Death was associated with age, treatment delay, HIV co-infection, and head of family's income. Main factors associated with negative treatment outcomes as a whole were age, HIV co-infection, illiteracy, alcoholism, and prior TB treatment. We suggest the following strategies to increase cure rates: further training of the Family Health Program personnel in TB control, awareness-raising on the need to tailor their activities to special care for cases (e.g., literacy training); targeting use of directly observed therapy for higher risk groups; establishment of a flexible referral scheme to handle technical and psychosocial problems, including alcoholism; and increased collaboration with the HIV/AIDS program

Fatores associados ao acesso geográfico aos serviços de saúde por pessoas com tuberculose em três capitais do Nordeste brasileiro

O objetivo do presente estudo foi identificar fatores associados ao acesso geográfico aos serviços de saúde por portadores de tuberculose em três capitais do Nordeste do Brasil. A amostra foi composta por casos novos de tuberculose, notificados em 2007. Foram utilizados dados provenientes do Sistema de Informação sobre Agravos de Notificação, e do Cadastro Nacional de Estabelecimento de Saúde. Os endereços dos domicílios e das unidades de saúde foram georreferenciados e, utilizando a distância entre o domicílio e a unidade de atendimento de cada caso, foi considerado acesso dificultado quando esta distância foi maior do que 800 metros. Foram estimadas as razões de prevalência bruta e ajustada por meio de regressão de Poisson. Verificou-se que após ajuste com as variáveis estudadas, apenas a variável unidade básica, em Salvador, Bahia (RP = 0,75; IC95%: 0,720-0,794) e em Recife, Pernambuco (RP = 0,402; IC95%: 0,318-0,508), manteve associação com o acesso dificultado. O estudo concluiu que a descentralização do atendimento em unidade básica pode contribuir com a melhoria do acesso aos serviços de saúde