Current Trends Influenza Activity -- Mississippi, United States, Worldwide

MISSISSIPPI

For the first time in several years, Mississippi experienced a major occurrence of influenza affecting schoolchildren. The outbreak of an influenza-like illness beginning the third week of January was first reported among elementary and junior high school children in Hancock County, where influenza type A(H1N1) virus was isolated. Soon thereafter, the Mississippi State Department of Health received reports of similar illnesses among schoolchildren in Lincoln, Hinds, Madison, Humphreys, and Washington Counties. Affected schools reported absenteeism of 20%-50%.

An epidemiologic investigation conducted in Hancock County Schools revealed symptoms of fever (97%), cough (91%), headache (90%), sore throat (81%), malaise (73%), and myalgia (68%) in children with illness, which developed abruptly and lasted 3-10 days. Fever commonly ranged from 38.3 C to 40.0 C (101 F to 104 F). Some patients also had abdominal pain (58%), nausea (52%), vomiting (39%), and diarrhea (28%) in varying degrees. During the outbreak, 444 of 1,093 students were absent from two schools. A follow-up of the absent students revealed that four were hospitalized when they developed pneumonia. Reported in Mississippi Morbidity Report by A Kennedy, MPH, R Farrell, B Helms, WE Riecken, Jr, MD, FE Thompson, MD, State Epidemiologist, Mississippi State Dept of Health; Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: This report documents the type of rapidly developing influenza outbreaks among schoolchildren caused by type A(H1N1) virus occurring in the present season. This activity, after a period of relative quiescence since A(H1N1) was most active in 1978-1979, might be related to the evolution of new antigenic variants (1) that spread to the United States, as well as to other genetic changes in the virus affecting transmissibility. The high proportion of children in this outbreak with gastrointestinal symptoms is not typical but has been previously reported when type A(H1N1) virus caused epidemics in 1978-1979 (2). UNITED STATES

Influenza activity continues to be reported in much of the United States, with spread of type A(H1N1) virus to the Pacific Northwest (Oregon and Washington); and type B virus, now identified from additional east-coast states (Connecticut, Delaware, North Carolina). However, there are indications that the overall level of influenza activity is decreasing. A smaller proportion of state health departments are now officially reporting regional or widespread influenza-like illnesses than previously (Figure 2), and this trend has been confirmed by an informal telephone survey of about 20% of state epidemiologists.

Reports from approximately 120 family practitioners participating in a pilot nationwide influenza morbidity surveillance system also show a decline in the number of patients with influenza-like illness (fever over 37.8 C (100 F) accompanied by at least one respiratory symptom) (Figure 3). The earliest and greatest rise in office visits to physicians for influenza-like illness had occurred in the South (including the combined South Atlantic, East South Central, and West South Central regions). This is consistent with reports of outbreaks and virus isolations earlier this season. Reports from physicians in these southern regions have shown a decrease in observed influenza-like illness over the past 4 weeks.

In other geographic areas, where physicians' reports suggest that influenza virus caused less morbidity than in the South, observed influenza-like illness has also recently decreased. However, it is possible this decreasing activity may change before the end of the influenza season because the regional prevalence of the active types A(H1N1) and B viruses may change independently. Low-level occurrence of type A(H3N2) infection continues, and such viruses have recently been isolated from patients in Indiana, New Hampshire, New York, and South Dakota. Reported by Collaborating Family Physicians in the Influenza Surveillance Network; US Air Force School of Aerospace Medicine, Brooks Air Force Base, Texas; State Epidemiologists and Laboratory Directors; Statistical Svcs Br, Div of Surveillance and Epidemiologic Studies, Epidemiology Program Office, Statistical Svcs Activity, and Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC. Editorial Note: When influenza type A(H1N1) virus predominates, as it most recently did in the 1978-1979 season, and outbreaks occur primarily in healthy young populations, influenza epidemics may not be reflected by increases in national mortality attributable to pneumonia and influenza, because the elderly are spared. Under such circumstances, it is especially useful to have a rapidly reported quantitative estimate of influenza morbidity. To answer this and other epidemiologic needs, a pilot study was initiated in the 1982-1983 season involving weekly reports from family practitioners in all regions of the country. The observations last year and thus far this year generally correspond with other indicators of influenza virus activity. Nevertheless, information from this system must be used cautiously because of the relatively small number of physicians, and because the communities served by the reporting physicians might not always represent major population centers in the nation. Also, the proportion of persons with influenza-like illness who visit their physicians could change as local outbreaks become known in a community. As with mortality data, long-term experience with the physician-reporting system is desirable to establish the limits within which its results can be reliably interpreted. WORLDWIDE

Since December 1983, influenza surveillance has indicated increased influenza type A(HlNl) and type B activity in some countries but little or no activity in other parts of the world. Influenza type A(H3N2) has been isolated less frequently and has usually been associated with sporadic cases.

Asia: Influenza type B was isolated from one patient in Yokohama, Japan, in February, while type A(H1N1) activity has continued at relatively high levels in many parts of the country. Influenza type B was also isolated from a few patients in Hong Kong and Singapore during November and December. In northern Pakistan, influenza type A(H3N2) has been associated with outbreaks affecting all age groups.

Australia: Influenza activity has been limited to a few sporadic cases. One case of influenza type A(H1N1) and one of type A(H3N2) have been confirmed by virus isolation since December 1983.

Africa: There continue to be few reports of influenza activity in Africa. Since January, type B has been isolated from only a few patients in Tunisia, and type A(H3N2) has been isolated from children and adults in Dakar, Senegal.

Central and South America: One influenza virus isolation from Central America has been reported; influenza type A(H3N2) was isolated from an infant in Honduras. There have been no reports from South America.

Europe: Reports from most European countries indicate little or no influenza activity. In England, influenza A(H1N1) was associated with an outbreak in a school; influenza B has been isolated from a few patients. In Italy, type A(H3N2) was isolated from two patients, and type A(H1N1), from one. The incidence of influenza-like illness has increased in the southeastern part of Norway, where influenza type B has been isolated, primarily from children 5-14 years of age. Type B virus has also been isolated in Yugoslavia; most of these isolates have been from school-aged children. In Czechoslovakia, influenza A(H1N1) has mainly been isolated from children in association with localized outbreaks. Influenza type A(H1N1) was also isolated from one patient in Finland, where local outbreaks of respiratory illness have occurred in military training centers; there have been no reports of widespread respiratory illnesses among the general population. A single isolate of type A(H1N1) has been reported from Sweden, where there is no general increase in influenza-like illnesses.

Union of Soviet Socialist Republics: Beginning in late November 1983, the incidence of influenza-like illness increased above expected levels in some parts of the Soviet Union. In Moscow, the incidence of illness increased in late December and peaked in the first week of February at a rate of 330 cases per 100,000 population. Activity has been primarily associated with type B, although type A(H1N1) has also been isolated. Most cases have occurred among children and young adults, with reports of localized outbreaks in schools. Reported by Virus Diseases Unit, World Health Organization, Geneva, Switzerland; WHO Collaborating Center for Influenza, Influenza Br, Div of Viral Diseases, Center for Infectious Diseases, CDC.

References

1. CDC. Antigenic analysis of recent influenza A(H1N1) viruses. MMWR 1983;32:534-5.

2. CDC. Influenza report no. 93. Issued January 1983.

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