Figure 5 is a histogram showing the number of stools that tested positive for Yersinia each month between 2010 and 2014, by type of test performed. The types of test include polymerase chain reaction, culture, or both polymerase chain reaction and culture. A line shows the total percent positivity for Yersinia. Prior to late 2013, all specimens were positive by culture alone. After polymerase chain reaction was introduced in late 2013, the total number of tests positive and percent positivity increased dramatically. Approximately 80% of specimens were positive by polymerase chain reaction alone and 20% were positive by culture and polymerase chain reaction together. Few specimens were positive by culture alone.