Classifying disease to map the way we live and die
There are few truer snapshots of a country’s wellbeing than its health statistics. While broad economic indicators such as Gross Domestic Product may skew impressions of individual prosperity, data on disease and death reveal how a population is truly faring.
The International Statistical Classification of Diseases and Related Health Problems (ICD) is the bedrock for health statistics. It maps the human condition from birth to death: any injury or disease we encounter in life − and anything we might die of − is coded.
Not only that, the ICD also captures factors influencing health, or external causes of mortality and morbidity, providing a holistic look at every aspect of life that can affect health.
Crucially, in a world of 7.4 billion people speaking nearly 7000 languages, the ICD provides a common vocabulary for recording, reporting and monitoring health problems. Fifty years ago, it would be unlikely that a disease such as schizophrenia would be diagnosed similarly in Japan, Kenya and Brazil. Now, however, if a doctor in another country cannot read a person’s medical records, they will know what the ICD code means.
Without the ICD’s ability to provide standardized, consistent data, each country or region would have its own classifications that would most likely only be relevant where it is used. Standardization is the key that unlocks global health data analysis.
Gender incongruence, meanwhile, has also been moved out of mental disorders in the ICD, into sexual health conditions. The rationale being that while evidence is now clear that it is not a mental disorder, and indeed classifying it in this can cause enormous stigma for people who are transgender, there remain significant health care needs that can best be met if the condition is coded under the ICD.
For mental health conditions, ICD codes are especially important since the ICD is a diagnostic tool, and thus, these are the conditions that often garner much of the interest in the ICD. These include gaming disorder, which evidence shows is enough of a health problem that it requires tracking through the ICD. Other addictive behaviours such as hoarding disorder are now included in ICD-11, and conditions such as ‘excessive sexual drive’ has been reclassified as ‘compulsive sexual behaviour disorder’.
A significant change in the mental disorders section of ICD-11 is the attempt of statisticians to simplify the codes as much as possible to allow for coding of mental health conditions by primary health care providers rather than by mental health specialists. This will be a critical move since the world still has a scarcity of mental health specialist – up to 9 out of 10 people needing mental health care don’t receive it.
History of the ICD
The history of the ICD traces back to England in the 16th century. Every week, the London Bills of Mortality would announce deaths from distinctly medieval causes: scurvy, leprosy, and the big killer – plague.
It wasn’t until the late 19th century though, when Florence Nightingale, just returned from the Crimean War, advocated for the need for gathering statistics on causes of disease and death that data began to be collected more systematically.
Around the same time French statistician Jacques Bertillon introduced the Bertillon Classification of Causes of Death, which was adopted by several countries.
In the 1940s, the World Health Organization took over Bertillon’s system and expanded it to include statistics on causes of injury and disease, producing the first version of the International Statistical Classification of Diseases, Injuries and Causes of Death (ICD). This allowed for the first time the collection of both morbidity and mortality data to map both disease trends and causes of death.
The data captured through ICD codes is of huge importance for countries. It allows for the mapping of disease trends and causes of death around the world, which are key indicators both of the health of a population, but also the social determinants that link closely to health, such as the education, nutrition, and public infrastructure - in short, a snapshot of where a country’s vulnerabilities lie.
A country in which people live in crowded, inadequate housing with no clean water are inevitably likely to have a higher incidence of diarrhoeal disease.
The Global Health Observatory is WHO’s gateway to health-related statistics for over 1000 indicators. Data coded through the ICD populates the Global Health Observatory allowing WHO to report World Health Statistics annually.
These statistics are critical in tracking progress towards key targets such as the Sustainable Development Goals.