Hurricane Isaac Will Not Worsen West Nile Virus Outbreak

August 29, 2012

August 29, 2012 — The West Nile virus outbreak of 2012 continues to grow at a record-setting pace, but the rain and floodwater from Hurricane Isaac will not make things worse, an official from the Centers for Disease Control and Prevention (CDC) said today.

The number of reported cases from August 21 to August 28 rose roughly 40%, to 1590, said Lyle Petersen, MD, MPH, director of the CDC's Division of Vector-Borne Infectious Diseases, in a press briefing. The year-to-date tally through August 28 is the highest for any year since the virus was first detected in the United States in 1999. The record for the most cases at is 9862 in 2003.

The number of deaths as of August 28 stood at 66, up 25 from a week earlier. The heaviest death toll occurred in 2002, when 284 people died. Fatalities typically occur among patients whose infection morphs into a neuroinvasive disease such as meningitis or encephalitis. Roughly 1 in 150 infected people develop such dangerous disorders.

Texas remains the epicenter of the outbreak of 2012, accounting for nearly half the reported cases and deaths. Forty-two other states and Washington, DC, also are contributing to the count.

The epidemic is peaking now, although northern states may experience a peak later than southern states, Dr. Petersen said. Because of the lag time between someone getting infected and them seeking medical care after symptoms emerge, the CDC expects the case count to keep on climbing for weeks to come.

Dr. Petersen said Hurricane Isaac, which hit southeast Louisiana last night, should not appreciably change the forecast for the West Nile virus outbreak, based on what has happened after previous hurricanes.

Although hurricanes can create pools of standing water where mosquitos breed, they also wipe out existing pools. Overall, "hurricanes and flood events tend to disrupt the entire ecology of the area, and thus interrupt this natural transmission cycle between birds and mosquitos that the virus normally exists in," he said. "The end result is that [they] do not have a major impact on...viral transmission."

However, the hurricane could have a minor effect. After Hurricane Katrina in 2005, the CDC noticed small upticks in the number of West Nile virus infections in areas of Louisiana where people became more exposed to infected mosquitos because they were either "living out in the elements" or working outdoors in reconstruction projects, Dr. Petersen said.

Individuals who live in the path of Hurricane Isaac, therefore, should take precautions such as wearing pants and long-sleeved shirts when outdoors at dawn and dusk, as well as using insect repellent.


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