Current Trends Late Season Influenza Type B Virus Activity --
United States
Despite a decline in levels of overall influenza activity,
reports
of influenza B virus activity increased during April and May.
Influenza B outbreaks in April or May have been reported in
California, New Mexico, North Dakota, Oregon, and Wisconsin,
including
two nursing home outbreaks in Napa and Solano counties, California.
These, and two earlier nursing home outbreaks reported from Maine
(1)
and New York, bring to four the number of influenza B outbreaks in
nursing homes reported this season. Other outbreaks in the above
states occurred predominately among children.
One outbreak affecting a younger population occurred on the
Fort
Totten reservation in North Dakota beginning mid-April and
continuing
for 2 weeks. Absentee rates in the reservation school (grades K-6)
peaked at 42%, compared with a normal absentee rate of 10%. All 16
teachers and the school principal also reported influenza-like
illness
during the outbreak. Records from the reservation clinic showed
that
patient visits had increased 49% during the outbreak and that
almost
all the increase was associated with influenza-like illness.
During
the outbreak, 52% of clinic visits were from patients 9 years of
age
or younger, and 40% of these involved influenza-like illness.
Influenza type B virus was isolated from specimens collected from
children with typical influenza during the outbreak.
Since April, 14 states have identified their first influenza
type
B isolates of the season; 13 states had identified type B isolates
before April.
Reported by W Freeman, MD, Ft. Totten Reservation, J Pearson, DrPH,
Acting State Epidemiologist, North Dakota State Dept of Health;
Respective state epidemiologists and laboratory directors; Div of
Surveillance and Epidemiologic Studies, Epidemiology Program
Office,
Statistical Svcs Activity, WHO Collaborating Center for Influenza,
Influenza Br, Div of Viral Diseases, Center for Infectious
Diseases,
CDC, D Streitz, North Dakota State Dept. of Health.
Editorial Note
Editorial Note: The report of late influenza B activity, including
several outbreaks, emphasizes the importance of maintaining
surveillance programs that include laboratory diagnosis for
respiratory virus outbreaks outside the fall and winter months.
For
example, confirmation of occasional outbreaks throughout the summer
months would provide one indicator that the implicated virus strain
is
likely to have a considerable impact in the next winter season.
"Early warning" has occurred in 2 recent years--with isolation of
influenza B/Singapore/222/79-like strains during summer 1979 and
influenza A/Bangkok/1/79-like strains during summer 1980.
Presently
available information, however, does not permit any reliable
prediction that influenza type B, rather than type A, will be
responsible for most influenza infections in the United States next
winter. As in other years, monitoring of influenza activity during
the next few months in countries with tropical climates (where
influenza tends to be endemic) and in the Southern Hemisphere, will
also be important in improving knowledge of the virus strain likely
to
appear in the United States next winter.
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