Outbreaks of type A(H1N1) influenza affecting primarily
children
and young adults are continuing. For the week ending January 17,
seven states* and Puerto Rico reported widespread outbreaks of
influenza-like activity, and 21 states** and the District of
Columbia
reported regional outbreaks of influenza-like illness. This is the
fourth week with more than 20 states reporting outbreak activity.
The
level of current activity is below the peak of the previous winter
when 37 states indicated outbreaks for one week in February.
For the report week ending December 31, the Centers for Disease
Control's sentinel physiciansS saw an average of 11.9 patients with
cases of influenza-like illness per week per physician; the average
was 9.1 for the report week ending January 7 (Figure 1). The
maximum
averages reported during influenza epidemics of the past three
winters
were between 11 and 12. The percentage of deaths associated with
pneumonia and influenza reported from 121 cities has remained below
the epidemic threshold (Figure 1).
Influenza A/Taiwan/86(H1N1)-like virus continues to be the
predominant strain of influenza this season and represents 99% of
isolates reported from collaborating diagnostic laboratories
(Figure
1). Forty-four states and the District of Columbia have now
reported
isolates of influenza A(H1N1) virusP. Influenza type A(H3N2) has
recently been reported from sporadically occurring cases in
Colorado
and in Texas; only one isolate (from Arizona) had been reported
previously this season. There have been no recent reports of type
B
virus isolates.
Reported by G Meiklejohn, MD, School of Medicine, Univ of Health
Sciences Center, Denver, Colorado; Influenza Research Center,
Baylor
College of Medicine, Houston, Texas; State and Territorial
Epidemiologists; State Laboratory Directors; WHO Collaborating
Center
for Influenza, Influenza Br, Div of Viral Diseases, Center for
Infectious Diseases, CDC.
*Colorado, Connecticut, Minnesota, Oregon, Texas, Washington, and
Wyoming.
**Alabama, Alaska, Arizona, California, Idaho, Iowa, Kansas,
Kentucky,
Maryland, Massachusetts, Montana, Mississippi, Nebraska, New
Mexico,
North Carolina, North Dakota, Pennsylvania, South Dakota, Virginia,
West Virginia, and Wisconsin.
SSentinel physicians are members of the American Academy of Family
Physicians who have agreed to report influenza-like activity to
CDC.
A case was defined as an instance of illness in a patient with
fever
greater than or equal to 37.8 C (100 F) and at least a cough or
sore
throat.
PLouisiana, North Dakota, Rhode Island, South Carolina, South
Dakota,
and Wyoming have not reported any influenza isolates so far this
season.
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