The Colorado Department of Public Health and Environment announced the increase on Monday. Colorado's Public Health Laboratory is using genetic testing to compare the bacteria isolated from people who test positive. Salmonella is common, and a month with more cases than usual could reflect multiple, unrelated infections from different foods. If sequencing shows that a large share of these isolates are nearly identical, that points toward a common source. Why Summer Counts Rise AnywaySalmonella cases increase every summer, and some portion of any July increase is expected.