The need for early detection of infectious diseases

Early detection of infectious diseases plays a crucial role in all treatment and prevention strategies. The diagram below illustrates a typical series of events following exposure to an infectious agent and the inherent time delay to a confirmed laboratory diagnosis. 

An incubation period follows the exposure event, where the infected person may be asymptomatic and unaware of their infection. Following the onset of symptoms, a variety of health behaviours and health encounters may occur depending on the severity of the symptoms. For example, searching for information on the internet, phoning NHS Direct or if symptoms are more serious, visiting their local GP or accident and emergency unit. There, an initial diagnosis will be made and samples may be sent off to laboratories for a definitive diagnosis. The time delay between exposure and confirmed diagnosis may be days, to weeks or months depending on the type infection. 

Rapid and accurate identification of the underlying agent (the bacterium or virus) using diagnostic testing is essential to select the correct control measure, such as containment, confinement, antimicrobials and vaccines. This is particularly true for emerging diseases, where we find ourselves in a race to develop new controls as the disease spreads. In an outbreak situation, vigilant monitoring is vital to inform us where to focus effort and assess the effectiveness of interventions.

Worldwide, however, many infections remain undetected. Due to poor diagnostic tools, infection is often undiagnosed and therefore untreated, or diagnosed at the late stage when treatment becomes less effective. This results in on-going transmission of serious infections, for example HIV, and delay in the identification of emerging threats, for example pandemic influenza, leading to major human and economic consequences for millions of people.