WHO influenza update dated 15th October 2018 shows that the National Influenza Centers (NICs) and other National Influenza Laboratories from 95 countries or territories reported data from 17 September 2018 to 30 September 2018. More than 58772 specimens were tested and 2124 showed positive for influenza viruses while influenza A was reported at 84.2% and influenza B at 15.8%. Of the subtypes influenza A viruses, 74% accounted for influenza A(H1N1)pdm09, 26% were influenza A(H3N2) and for B viruses 49% belonged to the B-Yamagata lineage and 51% to the B-Victoria lineage.

Overview of Influenza Surveillance in the United States

The influenza season is determined by the flu activity which varies from season to season with the activity starting to increase in October, peaking in December to February and continuing into May. For CDC, the reporting period for each season starts during Morbidity and Mortality Weekly Report (MMWR) week 40 and finishing week 39 of the following year. For the year 2018-2019, the season started on September 30, 2018, ending on September 28, 2019. As influenza is not a reported disease, the total number of people affected by it is not exactly known. However, the surveillance of the flu-related illness is conducted by the CDC through Outpatient Influenza-like Illness Surveillance Network (ILINet) and Flusurv-Net which procures the information on outpatient illness and on hospitalizations. In order to determine the burden of flu illness in the United States, a mathematical modeling is used in combination with the traditional flu surveillance systems. CDC collects information from different data sources to find out the influenza activity that is occurring, thereby monitoring influenza-related illness, the types of the influenza viruses circulating, monitoring the changes of the viruses and measuring the impact of the illness on hospitalizations and deaths. According to CDC estimates, influenza has resulted in around 9.3 million – 49.0 million illnesses, between 140,000 – 960,000 hospitalizations and between 12,000 – 79,000 deaths every year since 2010.

2018 – 2019 Influenza Season Week 42

Although in the United States, the influenza activity continues to remain low, the influenza A(H1N1)pfm09 viruses are identified as the most commonly circulating viruses by the public health laboratories. State health departments are responsible for reporting the influenza activity in their states every week through the State and Territorial Epidemiologists Reports. The state reports the activity of the illness as;

No activity – No laboratory-confirmed cases and no increase in the cases of influenza-like illness (ILI).

Sporadic – Either a single or a few-laboratory confirmed cases of influenza but no increase in the ILI cases.

Local – Outbreaks of influenza or the number of cases of ILI has increased and laboratory-confirmed cases of influenza in a single region of the state.

Regional – Outbreaks of influenza or increase in the number of ILI cases and recent laboratory-confirmed cases in at least two but less than half the regions of the state.

Widespread – Outbreaks of influenza or increase in the number of ILI cases and recent laboratory confirmed in at least half the regions of the state.

Geographic spread of Influenza

For the current Influenza season 2018 – 2018, week 42, the following influenza activity was reported;

  • Local influenza reported in four states namely Massachusetts, New Hampshire, North Dakota and Oregon.
  • Sporadic influenza reported in the District of Columbia, Puerto Rico, the U.S. Virgin Islands and 42 states namely; Alabama, Alaska, Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Florida, Georgia, Hawaii, Idaho, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Michigan, Minnesota, Missouri, Montana, Nebraska, Nevada, New Jersey, New Mexico, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Washington, West Virginia, Wisconsin, and Wyoming.
  • No influenza activity was reported by Illinois, Mississippi, Rhode Island and Virginia.
  • Guam did not report.

In this brief, we now look at some details of the weekly influenza report by the four states presenting local influenza activity.

  • North Dakota

According to the North Dakota Department of Health, the data collection for the season 2018- 2019 began on August 1, 2018, now continuing to week 42 of the current season. The influenza case count indicates a total of 122 numbers. The number of cases affected by Type A 2009 H1N1 virus is 13, Type A H3 is 2, Type A unspecified at 84 and Type B unspecified as 23 cases. The case statistics show a total of 4 hospitalized cases and the age group most affected were children under 10 years accounting for 59 cases. The county Benson shows the most affected number of cases accounting to a total of 49 cases followed by county Ramsey with a total of 21 cases.

  • Oregon

According to the Influenza Surveillance data from the Oregon Health Authority, for the current influenza season 2018 – 2019, week 41 data shows that the percentage of emergency department visits for ILI was at 0.9% and influenza-associated hospitalization was only 1. Of the total of 854 specimens tested at the labs, 10 (1.2%) showed positive specimens of which 100% of them were caused by Influenza type A. However, for the week 42, the percentage of emergency department visits for ILI was at 0.9% also and of the influenza tests conducted on a total of 974 specimens, 10 (1.0) were positive for influenza type A.

  • New Hampshire

According to the Weekly Influenza Surveillance Report by the New Hampshire Public Health Services, the influenza season began on the 9/30/2018 and continues through mid-May. For the week 41 report, a total of 4 specimens confirm positive and in all the cases influenza type A (H1N1)pdm09 was detected. An elevated level of acute respiratory Illness (ARI) is identified for three counties namely; Grafton, Sullivan and Strafford while moderate levels were evident in Carroll, Merrimack and Rockingham.

  • Massachusetts

For the 2018 – 2019 season, Massachusetts influenza activity at week 42 reports as local and five of the seven regions of Massachusetts reports increased ILI activity which are; West (1.44%), Central (1.26%), Northeast (2.22%), Boston (1.26%) and Southeast (1.42%).