The Hindu : Epidemiology intelligence

Online edition of India's National Newspaper
Tuesday, Oct 28, 2003

Opinion

Opinion - Leader Page Articles

Epidemiology intelligence

By T. Jacob John

Outbreaks of known diseases occur frequently but public health authorities fail to predict, prevent or interrupt them.

JUST AS crime remains a `mystery' until solved through `criminology intelligence', an outbreak of illness is also a `mystery' until it is solved through `epidemiology intelligence' (E.I.). Several outbreaks in India remain unsolved precisely for lack of E.I. The recent outbreaks in Andhra Pradesh, Maharashtra and Saharanpur district in Uttar Pradesh illustrate this point. Regarding the outbreak in Andhra Pradesh, The Hindu editorial of July 19 identified the need for "specialised testing facilities in the State to enable the Government to diagnose the disease in time and take swift, preventive action". Two questions come to mind: First, do we use the available national laboratories effectively? Second, will diagnosing the disease ensure swift preventive action? Outbreaks of known diseases, such as Japanese encephalitis (J.E.), dengue haemorrhagic fever (DHF) or Leptospirosis occur frequently, but public health authorities fail to predict, prevent or interrupt them.

An outbreak is clustering in time and space of `linked cases'. Most outbreaks, not all, are of infectious diseases. The Saharanpur outbreak was most probably not infectious. The description in the editorial of the "outbreak of the deadly virus which kills within 24 hours or less" is not characteristic of infectious disease, even of the brain, unless it is new . It appears that such unlinked cases were mixed up, causing confusion. If diseases that occur simultaneously are clubbed as one outbreak, diagnosis or identifying risk factors will be impossible. E.I. must establish criteria defining an `outbreak case' and those excluding it. If two or more diseases occur simultaneously, as in Andhra Pradesh, E.I. must enumerate cases of each disease and investigate it separately for risk factors.

`Public health' is all of Government action to prevent disease and promote health. Outbreaks tend to affect the socio-economically underprivileged more than the well to do. Equity demands good public health. Epidemiology is the foundation science of public health. The tool of public health to detect and intercept outbreaks is E.I., a branch of epidemiology. A disease surveillance system is essential to provide `early warning signals' of outbreaks. Every civilised country has such a system, but not India. Epidemiology is the systematic study of the distribution and determinants of health problems. The determinants of a disease are the cause (aetiology, in medical parlance) and the risk factors (conditions leading to exposure to infection, to actual infection, or to the disease when infected). Risk factors determine why some persons fall ill while others do not. Public health must disseminate authentic information for professionals and the public to avoid risk factors.

The discipline of E.I. must be established in India to address outbreaks that recur almost every year. Our dismal track record of not solving them bears testimony to the lack of E.I. State institutes of E.I. must be established and public health personnel trained. The speed in detecting Severe Acute Respiratory Syndrome (SARS) as a new entity, identifying its mode of transmission and applying preventive measures offers lessons for India. In short, prevention of transmission requires the definition of transmission routes, which is the task of E.I. Five years ago, an outbreak of a fatal encephalitis occurred in Malaysia, at first suspected to be J.E. It was quickly found that it was not mosquito-borne, but transmitted via contact with respiratory secretions of sick pigs. The information was sufficient to prevent further cases. Eventually the cause was discovered to be a new virus caused by fruit bats (flying foxes), now named Nipah. Its transmission route was from bats to pigs to humans and then human-to-human. Authentic and detailed reports on SARS, Nipah, Ebola virus disease, HIV/AIDS etc., are available in professional journals for study, scrutiny and further research. This is not the case in most Indian outbreaks.

The Siliguri outbreak in 2001 affected 60 adults, killing 36, most of them health care workers. Five institutions/organisations investigated the outbreak, without coordination or cooperation, but the clinical description or risk factors have not been published in a medical journal so far. One group claimed it was measles, others called it Hantavirus Pulmonary Syndrome. The clinical picture resembled Nipah virus disease, but will we ever know the truth? The 1994 Surat outbreak of what was called pneumonic plague caused panic in India and abroad, and a financial loss of an estimated $ 3 billion.

Pneumonic plague has not been reported without bubonic plague, which did not occur in Surat. Pneumonic plague is transmitted human-to-human, but no `case' had contact with another `case'. Microbiologists published finding plague bacteria, but even rudimentary E.I. was not applied. Some outbreaks are new diseases or due to new or resurgent microbes, such as Ebola, SARS, Nipah, DHF, etc. E.I. must first identify the disease as new before looking for the unknown microbe. Discovering the agent by sophisticated laboratory investigations may take time. If the disease is new, we can get help from national/international laboratories to track the aetiology. But prevention need not wait. E.I. must identify the transmission pathway of the unknown agent. Risk factors determine the remedial measures that must be applied to control the outbreak, even though the microbe (or possible chemicals causing toxic disease such as Reye's syndrome — the 24-hour killer) has not yet been identified. Killing pigs en masse, or spraying/fogging insecticides should not happen without established need and evaluation. The microbe that fits the transmission pathway is the most likely cause of the outbreak. It is not too late to apply E.I. and solve the mystery of the recent childhood killer brain disease in Andhra Pradesh.

(The writer is a Retired Professor of Virology, Christian Medical College, Vellore.)

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