Bacteria Water

Virginia Department of Health closes investigation of Lake Anna Memorial Day outbreak

The Virginia Department of Health (VDH) reports that the most recent testing of water samples collected from Lake Anna did not detect the presence of Shiga toxin-producing Escherichia coli (STEC) O157. Additional fecal bacteria results for the water samples did not show levels that typically rise to public health concern. VDH reminds the public that the upper section of North Anna Branch of Lake Anna in Louisa County remains under a swimming advisory due to harmful algal blooms (HABs) not related to this STEC outbreak.

VDH is concluding the STEC outbreak investigation associated with exposure to Lake Anna over the Memorial Day weekend. It has been more than 20 days (two ten-day incubation periods) since the last person who visited Lake Anna over the holiday became ill. Laboratory testing by the Virginia Department of General Services Division of Consolidated Laboratory Services (DCLS) was not able to identify STEC O157 bacteria in water samples from the lake. Additionally, VDH was not able to identify the source of the bacteria in the water.

Water testing is a snapshot in time and at a specific location. The samples used for STEC testing were collected about four weeks after the Memorial Day Weekend and might not reflect the water environment during the holiday weekend. These results also cannot predict future risk. Swimming or other activities in any natural body of water always pose some health risk because the water is not disinfected. Children under the age of five years, older adults, and those with weakened immune systems are at higher risk of contracting illness from natural bodies of water.

VDH will conduct enhanced public health surveillance through July 17, because of anticipated upcoming Fourth of July celebrations. Information will be provided as it develops. This surveillance involves monitoring emergency department and urgent care visits, in addition to investigating any STEC case reported by a healthcare provider. VDH and its local health departments will continue to work with local partners to better understand potential risks in the area and prevention strategies to address those risks. DEQ will continue the routine bacterial monitoring of Lake Anna that occurs each year between April and October. This monitoring includes testing for fecal bacteria, but not STEC. The DEQ results are available at Water Quality Data Home.

To prevent illness when swimming, boating, wading, or recreating in natural bodies of water, people should:

  • Never swallow untreated water and don’t swim if your skin has cuts or open wounds.
  • Wash hands frequently, including after swimming and before preparing and eating food.
  • Shower or bathe after swimming to wash off possible germs and contaminants.
  • Check the water and the area around it before swimming. Avoid going in water if there is a green film on the water or if the water is cloudier than usual. Avoid swimming near storm drains or livestock.
  • Avoid swimming if you are vomiting or have diarrhea.
  • Avoid swimming for three days after a heavy rain. Heavy rain picks up anything it comes in contact with, including germs from overflowing sewage, polluted storm water, and runoff from land.
  • Properly dispose of human waste by discharging boat sewage at marinas with a pump-out unit or dump station.
  • Check with your healthcare provider before swimming in oceans, lakes, rivers, and other natural bodies of water if your body’s ability to fight germs is already affected by other health problems or medicines.

VDH and the Virginia Harmful Algal Bloom Task Force will continue to monitor water quality in the lake for HAB. In general, advisories will be lifted following two consecutive test results with acceptable levels for algal cell counts and/or toxin concentration. More recommendations for healthy practices during water activities are available at and CDC’s How to Safely Visit Oceans, Lakes, and Rivers website.