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Influenza Season Has Officially Begun, CDC Says

Troy Brown, RN
December 21, 2018

The 2018-2019 influenza season has officially begun, according to the Centers for Disease Control and Prevention (CDC).

"Increases in flu activity summarized in CDC's most recent FluView report, including increases in influenza-like illness (ILI) and the proportion of laboratory-confirmed flu cases nationally, have signaled the start of the 2018-2019 influenza season," the CDC reports.

The proportion of outpatient visits for influenza passed the national baseline for the second time this season, with high activity in Georgia and Colorado and widespread activity in Guam and six states, according to the CDC's most recent FluView report.

The reported cumulative rate of laboratory-confirmed influenza-associated hospitalizations was 2.9 per 100,000 population, up from 1.9 per 100,000 population during week 49.

Children younger than 5 years old had the highest hospitalization rate, at 7.7 per 100,000 population.

The proportion of deaths resulting from pneumonia and influenza during the week ending December 8 (week 49) was 6.0%, which was below the National Center for Health Statistics Mortality Surveillance System's epidemic threshold of 6.7% for week 49.

The CDC received a report of one influenza-associated pediatric death during week 50. The child's death occurred during the week ending December 8 (week 49) and was associated with an influenza A virus for which no subtyping was performed. Seven children have died from influenza-associated complications this season.

Influenza A viruses have predominated in the United States since early October, with influenza A(H1N1)pdm09 predominating in most of the country. In the southeastern United States (Health and Human Services Region 4); however, influenza A (H3) viruses have been the most commonly reported viruses for the most recent 3 weeks.

The percentage of respiratory specimens in clinical laboratories that are testing positive for influenza is rising.

The majority of the influenza viruses characterized antigenically and genetically are similar to cell-grown reference viruses representing the viruses used in the 2018-2019 Northern Hemisphere influenza vaccines.

All influenza viruses tested since late May have been susceptible to the antiviral medications oseltamivir, zanamivir, and peramivir.

National Activity

Colorado and Georgia reported high ILI activity during the week ending December 15 (week 50), marking the fourth week in a row for Georgia. Georgia was the only state with high ILI activity during week 49. Louisiana reported high ILI activity during week 47 and 48, and moderate ILI activity during week 49.

The proportion of outpatient healthcare visits for ILI was 2.7% during week 50, surpassing the national baseline of 2.2%. That proportion exceeded the national baseline during week 47, rising to 2.3% before settling at 2.2% for weeks 48 and 49. The percentage of outpatient visits for ILI was at or above the region-specific baseline in eight of 10 regions, compared with five of 10 regions during week 49.

New York City and nine states (Alabama, Arizona, Arkansas, Kentucky, Louisiana, Missouri, New Jersey, South Carolina, and Virginia) reported moderate ILI activity during week 50 compared with Puerto Rico and four states (Colorado, Connecticut, Kentucky, and Louisiana) during week 49. Two states (Colorado and South Carolina) and three states (Alabama, Oklahoma, and Utah) reported moderate ILI activity during weeks 48 and 47, respectively.

Geographic spread of influenza was widespread in Guam and six states (Alabama, California, Delaware, Georgia, Massachusetts, and New York) in week 50, up from three states (California, Georgia, and Massachusetts) during week 49, and only Massachusetts during week 48. No state reported widespread activity during week 47. Widespread activity means a state is having outbreaks of flu and laboratory-confirmed flu in half or more regions of the state.

Eighteen states (Arizona, Connecticut, Florida, Idaho, Kentucky, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, North Carolina, Ohio, Oregon, Pennsylvania, Rhode Island, Texas, Vermont, and Virginia) reported regional influenza activity during week 50. That number has risen steadily during the last four weeks, from five states (Connecticut, Kentucky, Massachusetts, Oregon, and Utah) during week 47, nine states (California, Connecticut, Georgia, Kentucky, Louisiana, Nevada, New York, Oregon, and Vermont) during week 48, and 10 states (Arizona, Connecticut, Idaho, Kentucky, Nevada, New York, North Carolina, Rhode Island, Texas, and Vermont) during week 49.

Regional activity indicates influenza activity is occurring in two or more but fewer than half of the regions of the state.

Local activity was reported by 19 states and sporadic influenza activity was reported by the District of Columbia, Puerto Rico, US Virgin Islands, and seven states.

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Reviewed on 12/24/2018

SOURCE: Medscape, December 21, 2018. CDC Weekly US Influenza Surveillance Report. Published online December 21, 2018.

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