Last week a clean, near perfect trial. This week research conducted in the chaotic world of a cholera outbreak. But this is important stuff - as the authors say, we need to know what happens under field conditions. The basic method is simple - a case control study, comparing the vaccination history of cases (patients with cholera) versus controls (people without cholera). But in field conditions it's not so easy to tell whether people actually have cholera or not, and whether they've been vaccinated or not. So there are various extra study elements built in to cope with that.