open reading frame) in addition to the usual IS1016-bexA deletion ...

Figure 1. The number of patients in each season surveyed by the date of onset of influenza A
or influenza B. Percentages are the percentage of all seasonal cases of influenza attributable to
influenza B. Median, median date of epidemic, expressed as month/day.
with use of the commercial rapid detection
kits in the participating clinics throughout
Japan between 10 November and 31 May
every year. Figure 1 shows the date of onset
and the number of cases of influenza A
or influenza B that were diagnosed with
the use of rapid detection kits during the
past 5 influenza seasons. The total number
of influenza A or influenza B cases, the
percentage of cases that are attributable to
influenza B, and the median date of the
epidemic in each season are also shown.
The prevalence of influenza A was consistent
in almost every year. However, the
prevalence of influenza B was variable season
by season. The percentage of influenza
cases attributable to influenza B was very
small in the 2003–2004 and 2005–2006
seasons (2.5% and 2.1%, respectively).
However, in the 2004–2005 season, the
number of influenza B cases was more
than twice the number of influenza A
cases; the percentage of influenza cases attributable
to influenza B was 67.8%. The
high incidence of influenza B during the
2004–2005 season in Japan (also available
on the Web site of the Infectious Disease
Surveillance Center of Japan [3]) seemed
to be unusual, as mentioned by Baum [1].
We would also like to emphasize that
all patients from whom we obtained the
date and time of the onset of fever, the
administration of oseltamivir, and the resolution
of fever were included in the study,
and no patients with influenza A or influenza
B from whom we obtained these data
were excluded [2].
In the 2004–2005 season, influenza A
and influenza B were almost simultaneously
prevalent (the median dates of the
epidemics were 27 February for influenza
A and 21 February for influenza B). It
seems to be important to differentiate patients
with influenza A from patients with
influenza B by use of commercial antigen
detection kits, particularly during seasons
in which both types of influenza virus are
simultaneously prevalent (such as the
2004–2005 season), because oseltamivir is
less effective for the treatment of influenza
B virus, as reported elsewhere [2, 4].
Acknowledgments
Potential conflicts of interest. All authors: no
conflicts.
Naoki Kawai, 1 Hideyuki Ikematsu, 1,2
Norio Iwaki, 1 Nobuo Hirotsu, 1 and
Seizaburo Kashiwagi3 1Japan Physicians Association, Tokyo, and
2
Department of Clinical research, Hara-doi Hospital,
and 3 Fukuoka Red Cross Blood Center,
Fukuoka, Japan
References
1. Baum SG. Oseltamivir and the influenza alphabet.
Clin Infect Dis 2006; 43:445–6.
2. Kawai N, Ikematsu H, Iwaki N, et al. A comparison
of the effectiveness of oseltamivir for
the treatment of influenza A and influenza B:
a Japanese multicenter study of the 2003–2004
and 2004–2005 influenza seasons. Clin Infect
Dis 2006; 43:439–44.
3. Infectious Disease Surveillance Center of Japan.
Weekly reports of virus isolation/detection
2002/03–2006/07. Available at: https://hassei
doko.mhlw.go.jp/Byogentai/Pdf/data2e.pdf.
Accessed 20 September 2006.
4. Kawai N, Ikematsu H, Iwaki N, et al. Factors
influencing the effectiveness of oseltamivir and
amantadine for the treatment of influenza: a
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