CDC says West Nile activity may have peaked

Sep 12, 2012 (CIDRAP News) – Federal health officials today said the worst of the nation's West Nile virus (WNV) outbreak appears to be over but warned that cases will continue to add up at a pace on track to make 2012 a record year.

Lyle Petersen, MD, MPH, director of the Center for Disease Control and Prevention's (CDC's) Division of Vector-Borne Diseases, at a media briefing today said that although the number of new cases rose 35% in the past week, health officials are seeing signs that WNV activity has peaked. He noted that illness and death reports are lagging indicators and that the CDC expects to keep receiving a high volume of reports until October.

The CDC said today it has received reports of 2,636 cases so far, an increase of 643 from the previous week. The number of neuroinvasive disease cases rose by 336, to 1,405, and the number of deaths climbed to 118, with 31 of them reported over the past week.

Petersen said the number of neuroinvasive cases is thought to be the best indicator of the scale of the epidemic, because those types of WNV infections are more consistently reported than the less severe West Nile fever, for which a fraction of infected patients seek medical care. The number of neuroinvasive cases is the highest reported for this time in September since the disease was first detected in the United States in 1999.

Though he said the number of overall cases is behind the pace for 2003 due to an artifact in case reporting, "We still believe this year's outbreak is the most serious reported."

Two thirds of the cases have been reported by the same six states that continue to report the highest numbers: Texas, South Dakota, Mississippi, Oklahoma, Louisiana, and Michigan. So far, 40% of the nation's cases have been in Texas, especially in the Dallas County area.

As of yesterday, the Texas Department of State Health Services (TDSHS) reported 1,150 WNV infections, which includes 564 neuroinvasive disease cases and 50 deaths.

Roger Nasci, PhD, chief of the CDC's arboviral diseases branch in the Division of Vector-Borne Diseases, told reporters that a temporary shortage of West Nile virus testing kits that surfaced last week has been resolved, and that labs and providers are anticipating that they should be able to meet the demand for the rest of the season.

A surge in WNV cases over the summer at one point halted testing at some commercial and local labs and prompted one hard-hit state—Oklahoma—to warn providers to reserve the test for the sickest patients. The main company that makes the tests, Focus Diagnostics, received approval for a new lot of kits, which allowed it to quickly fill back orders, according to previous reports.

In the meanwhile, the CDC and the Association of Public Health Laboratories (APHL) held a conference call with providers and stakeholders to coordinate testing resources and discuss the outbreak and the projected supply.

See also:

CDC WNV home page, with today's updated case count

TDSHS WNV case total

Sep 7 CIDRAP News story "West Nile surge pushes supply of test kits"

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