Differences in clinical features between influenza A H1N1, A H3N2, and B in adult patients

Objective: The differences in clinical features between influenza A H1N1, A H3N2, and B in the past three influenza seasons were examined.
Methodology: Patients with respiratory symptoms who consulted Kurume University Medical Center, Department of Internal Medicine, Kurume, Fukuoka, Japan, from January to March in 1999, 2000, and 2001 were included. Based on virological and serological findings, the influenza patients were divided into the above three groups for comparison of symptoms and laboratory data.
Patients: (n = 196) included 54 with influenza A H1N1, 98 with A H3N2, and 44 with B. Mean ages in the groups were 33 +/- 8.4 years, 41 +/- 15.2 years, and 29 +/- 9.8 years (influenza B patients tended to be younger). Fever was much greater in the A H3N2 group (38.6 +/- 0.46 degrees C) than in the A H1N1 or B groups. This was also true for laboratory indices of viral infection. Gastrointestinal symptoms such as nausea, epigastralgia, and diarrhoea were prominent in influenza B. Myalgia was common in all groups.
Conclusions: Influenza A H3N2 infection was more severe than A H1N1 or B in terms of fever, leukopenia, and C-reactive protein. Myalgia and other symptoms such as fever, headache, general malaise and sore throat were equally frequent in influenza A H3N2, A H1N1, and B infections. Gastrointestinal symptoms were more common in influenza B.