Abstract A serological survey was carried out in Monteria (500 000 population), a mid-size city in Colombia. An overall prevalence of 55.3% (95% confidence interval, 52.5%–57.8%) was found among a sample of 1.368 people randomly selected from the population. Test positivity was related to economic characteristics with the highest prevalence found in the most impoverished areas, representing 83.8% of the city’s population. We found a prevalence that might be associated with some important level of population immunity.