Update: Influenza Activity — United States, October 1–November 25, 2017

Outpatient Illness Surveillance

During October 1–November 25, 2017, the weekly percentage of outpatient visits for influenza-like illness (ILI) to heath care providers participating in the U.S. Outpatient Influenza-like Illness Surveillance Network (ILINet) ranged from 1.3% to 2.3%. During the week ending November 25, 2.3% of patient visits reported through ILINet were for ILI, which is above the national baseline** level of 2.2% (Figure 4). The increase in the percentage of patient visits for ILI during the week ending November 25 (surveillance week 47) might be influenced in part by a reduction in routine health care visits during the holidays, as has occurred in previous seasons. During the week ending November 25, four of 10 U.S. Department of Health and Human Services regions†† (Regions 1, 4, 6, and 7) reported a percentage of outpatient visits for ILI at or above their region-specific baseline levels.

ILINet data are used to produce a weekly jurisdiction-level measure of ILI activity,§§ ranging from minimal to high. For the week ending November 25, three states (Louisiana, Mississippi, and South Carolina) experienced high ILI activity; one state (Georgia) experienced moderate ILI activity; 10 states (Alabama, Alaska, Arizona, Hawaii, Massachusetts, Nebraska, Oklahoma, South Dakota, Texas, and Virginia) experienced low ILI activity; the District of Columbia, New York City, and 36 states (Arkansas, California, Colorado, Connecticut, Delaware, Florida, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oregon, Pennsylvania, Rhode Island, Tennessee, Utah, Vermont, Washington, West Virginia, Wisconsin, and Wyoming) experienced minimal ILI activity; and Puerto Rico had insufficient data to calculate an ILI activity level.

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