Table 1 Patient characteristics

Age (average ± S.D.)

39.3  ± 21.2

44.6  ± 16.6

2.9  ± 2.9

43.5  ± 24.0

 Under 16 years old

37 (15.2%)

4 (2.0%)

31 (100%)

2 (18.2%)

Gender, female

138 (56.6%)

119 (58.9%)

14 (45.2%)

5 (45.5%)

Underlying diseases

81 (33.2%)

75 (37.1%)

3

(9.7%)

3 (27.3%)

History of Influenza vaccination

122 (50.0%)

102 (50.5%)

14 (45.2%)

6 (54.5%)

Time since onset of symptoms

 0–6 h

33 (13.5%)

26 (12.9%)

5 (16.1%)

2 (18.2%)

 6–12 h

31 (12.7%)

21 (10.4%)

9 (29.0%)

1 (9.1%)

 12–24 h

104 (42.6%)

86 (42.6%)

13 (41.9%)

5 (45.5%)

 24–48 h

45 (18.4%)

41 (20.3%)

3 (9.7%)

1 (9.1%)

 48–72 h

21 (8.6%)

20 (9.9%)

1 (9.7%)

0 (0.0%)

 72 h -

7 (2.9%)

6 (3.0%)

0 (0.0%)

1 (9.1%)

 Unknown

3 (1.2%)

2 (1.0%)

0 (0.0%)

1 (9.1%)

Symptoms

 Fever

227 (93.0%)

186 (92.1%)

31 (100%)

10 (90.9%)

 Fatigue

194 (79.5%)

177 (87.6%)

1 (3.2%)

8 (72.7%)

 Nasal discharge

158 (64.8%)

128 (63.4%)

20 (64.5%)

10 (90.9%)

 Cough

157 (64.3%)

137 (67.8%)

18 (58.1%)

2 (18.2%)

 Headache

152 (62.3%)

144 (71.3%)

1 (3.2%)

7 (63.6%)

 Sore throat

150 (61.5%)

141 (69.8%)

2 (6.5%)

7 (63.6%)

 Arthralgia

129 (52.9%)

124 (61.4%)

0 (0.0%)

5 (45.5%)

 Myalgia

97 (39.8%)

92 (45.5%)

9 (29.0%)

4 (36.4%)

 Diarrhea

15 (6.1%)

14 (6.9%)

1 (3.2%)

1 (9.1%)

 Nausea

13 (5.3%)

11 (5.4%)

0 (0.0%)

1 (9.1%)

Results of influenza antigen test using silver amplification immunochromatography

 Influenza A

93 (38.1%)

84 (41.6%)

5 (16.1%)

4 (36.4%)

 Influenza B

1 (0.4%)

1 (0.5%)

0 (0.0%)

0 (0.0%)

 Negative

150 (61.5%)

117 (57.9%)

26 (83.9%)

7 (63.6%)

Clinical diagnosis

 Influenza

108 (44.3%)

98 (48.5%)

6 (19.4%)

4 (36.4%)

 Acute upper respiratory infection

105 (43.0%)

77 (38.1%)

21 (67.7%)

7 (63.6%)

 Acute bronchitis

17 (7.0%)

14 (6.9%)

3 (9.7%)

0 (0.0%)

 Others

14 (5.7%)

13 (6.4%)

1 (3.2%)

0 (0.0%)