There is a very controversial and highly cited 2006 British Medical Journal (BMJ) article called “Googling for a diagnosis – use of Google as a diagnostic aid: internet based study” which concludes that, for difficult medical diagnostic cases, it is often useful to use Google Search as a tool for finding a diagnosis. Difficult medical cases are often represented by rare diseases, which are diseases with a very low prevalence.

The authors use 26 diagnostic cases published in the New England Journal of Medicine (NEJM) in order to compile a short list of symptoms describing each patient case, and use those keywords as queries for Google. The authors, blinded to the correct disease (a rare diseases in 85% of the cases), select the most ‘prominent’ diagnosis that fits each case. In 58% of the cases they succeed in finding the correct diagnosis.

Several other articles also point to Google as a tool often used by clinicians when searching for medical diagnoses.

But is that so convenient, is that enough, or can this process be easily improved? Indeed, two major advantages for Google are the clinicians’ familiarity with it, and its fresh and extensive index. But how would a vertical search engine with focused and curated content compare to Google when given the task of finding the correct diagnosis for a difficult case?

Well, take an open-source search engine such as Indri, index around 30,000 freely available medical articles describing rare or genetic diseases, use an off-the-shelf retrieval model, and there you have Zebra. In medicine, the term “zebra” is a slang for a surprising diagnosis. In comparison with a search on Google, which often returns results that point to unverified content from blogs or content aggregators, the documents from this vertical search engine are crawled from 10 web resources containing only rare and genetic disease articles, and which are mostly maintained by medical professionals or patient organizations.

Evaluating on a set of 56 queries extracted in a similar manner to the one described above, Zebra easily beats Google. Zebra finds the correct diagnosis in top 20 results in 68% of the cases, while Google succeeds in 32% of them. And this is only the performance of the Zebra with the baseline relevance model — imagine how much more could be done (for example, displaying results as a network of diseases, clustering or even ranking by diseases, or automatic extraction and translation of electronic health record data).