Shortly after a backpacking trip in Michigan in 2009, 20-year-old Sarah Sheridan came down with what seemed to be a nasty case of the flu. Unlike the flu, however, her symptoms only got worse with time. Blood tests, MRI scans, spinal taps and other investigations came back normal or inconclusive.

Sheridan spent the next three years in and out of hospital, all to no avail. Her insurance claims swelled to over $100,000. It wasn’t until a chance encounter with someone who’d had Lyme disease that she finally found relief.

New web-based tools seek to spare others from a similar ordeal. CrowdMed, launched on 16 April at the TedMed conference in Washington DC, uses crowds to solve tough medical cases.

Anyone can join CrowdMed and analyse cases, regardless of their background or training. Participants are given points that they can then use to bet on the correct diagnosis from lists of suggestions. This creates a prediction market, with diagnoses falling and rising in value based on their popularity, like stocks in a stock market. Algorithms then calculate the probability that each diagnosis will be correct.