|Values are valid only on day of printing.|
Influenza is usually a mild illness of the upper respiratory tract. Involvement of the lower respiratory tract, however, can lead to 4 types of clinical syndromes: physical signs of lower respiratory tract involvement without roentgenographic evidence of pneumonia, influenza complicated by bacterial pneumonia, primary influenza virus pneumonia, and combined influenzal and bacterial pneumonias.
Influenza virus infections are most severe in patients with certain preexisting conditions such as rheumatic heart disease, bronchopulmonary disease, impaired renal function, and diabetes mellitus. Infections can be more severe in elderly patients, pregnant females, and immunocompromised patients.
Influenza virus type A can produce serious illness during the first 2 years of life, with croup, bronchitis, and pneumonia being prominent.
Influenza A may also precipitate asthmatic attacks and produce chronic pulmonary complications in children.
The presence of IgM class antibody or a 4-fold or greater rise in titer in paired (acute and convalescent) sera indicates recent infection.
The presence of IgG class antibody generally indicates past exposure.
Influenza virus infections occur exclusively from November through March.
1. Rothbarth PH, Groen J, Bohnen AM, et al: Influenza virus serology-a comparative study. J Virol Methods 1999;78:163-169
2. Pachucki CT: The diagnosis of influenza. Semin Resp Infect 1992;7:46-53
3. Wendt CH: Community respiratory viruses: organ transplant recipients. Am J Med 1997;102:31-36