Simple public health measures, such as the isolation of individuals with disease symptoms and the tracing and quarantining of anyone who has been in contact with them, are the most effective ways of stopping many infectious diseases, according to mathematical modelling by a team of Imperial College London researchers.
The research, published in the latest Proceedings of the National Academy of Sciences, examines how effective simple public health measures are when confronted with a variety of infectious diseases. The team identified how infectious certain diseases are, how long before symptoms show, and how they would affect an individual’s behaviour.
They compared two moderately transmissible viruses, SARS and HIV, and two highly transmissible viruses, smallpox and pandemic influenza. They calculated that both SARS and smallpox could be effectively contained through simple public health measures. However, while control of SARS can be achieved solely by isolating diagnosed cases, smallpox control additionally requires contacts of cases to be traced and isolated. In contrast, pandemic influenza and HIV could not be stopped by these measures as many infections occur before symptoms are shown.
Dr Christophe Fraser from Imperial College London, based at St Mary’s Hospital, and one of the authors of the research, says: "This study is the first time research has combined both biological information about infectious diseases, and behavioural information. As well as looking at the infectiousness of the disease, we also considered behavioural factors, such as whether infected individuals would begin to isolate themselves as the disease began to affect them. For example, with smallpox, symptoms are preceded by a fever, which would result in many of those infected effectively quarantining themselves through being too ill to leave the house."
"Previously, government health policies for dealing with a smallpox outbreak have involved mass vaccination of the population, but this study has shown that identification and isolation of infected individuals and their contacts would be sufficient to stop the spread."
The researchers developed a mathematical model of infectious disease outbreaks using previously published studies that had captured the distribution times of symptoms and infectiousness of the disease.
They also found that the success of control measures was determined as much by the amount of disease transmission before symptoms were displayed, as how easily the disease is transmitted.
Imperial College, University of London. May 2004.