Table 1.
Patients with H1N1 Virus Infection (H1N1 Group) Compared with Patients Presenting with an Influenza-Like Illness who had Negative Real-Time Reverse-Transcriptase Polymerase Chain Reaction Results for Influenza (Influenza-Negative Group) and Patients with H3/B Seasonal Influenza (H3/B Group)
| Characteristic | H1N1 group (n = 97) | Influenza negative group (n = 641) | Pa | Influenza H3/B group (n = 26) | Pb |
|---|---|---|---|---|---|
| Demographic characteristic | |||||
| Age | |||||
| Median years (IQR) | 21 (15–25) | 20 (4–30) | .15 | 16 (10–20) | .003 |
| <2 years | 2/97 (2) | 78/641 (12) | <.01 | 0/26 (0) | .001 |
| 2–17 years | 25/97 (26) | 210/641 (33) | 17/26 (65) | ||
| 18 to 24 years | 43/97 (44) | 117/641 (18) | 6/26 (23) | ||
| 25–49 years | 26/97 (27) | 173/641 (27) | 2/26 (8) | ||
| ≥50 years | 1/97 (1) | 63/641 (10) | 1/26 (4) | ||
| Male sex | 73/97 (75) | 317/641 (49) | <.01 | 15/26 (58) | .09 |
| Race/ethnicity | <.01 | .02 | |||
| White | 23/60 (38) | 155/331 (47) | 10/18 (56) | ||
| Black | 16/60 (27) | 39/331 (12) | 3/18 (17) | ||
| Hispanic | 9/60 (15) | 16/331 (5) | 0/18 (0) | ||
| Pacific Islander | 10/60 (16) | 46/331 (14) | 1/18 (6) | ||
| Other | 2/60 (3) | 75/331 (23) | 4/18 (22) | ||
| Duty status | <.01 | <.01 | |||
| Active duty | 60/97 (62) | 174/641 (27) | 5/26 (19) | ||
| Family member | 36/97 (37) | 440/641 (69) | 19/26 (73) | ||
| Retiree | 1/97 (1) | 27/641 (4) | 2/26 (8) | ||
| Exposure history | |||||
| Travel to Mexico | 1/97 (1) | 15/641 (2) | .71 | 0/26 (0) | >.99 |
| Contact with H1N1 virus infection | 50/97 (52) | 40/641 (6) | <.01 | 1/26 (4) | <.01 |
| Contact with ILI | 56/97 (58) | 143/641 (22) | <.01 | 8/26 (31) | .04 |
| Current tobacco use | 15/82 (18) | 60/499 (12) | .15 | 2/22 (9) | .52 |
| Medical history | |||||
| Asthma | 17/94 (18) | 94/602 (16) | .55 | 2/26 (8) | .36 |
| COPD | 0/94 (0) | 4/602 (1) | >.99 | 0/26 (0) | … |
| Heart disease | 1/94 (1) | 13/602 (2) | .71 | 0/26 (0) | >.99 |
| Diabetes | 2/94 (2) | 29/602 (5) | .42 | 0/26 (0) | … |
| Pregnancy | 4/97 (4) | 1/613 (0.2) | <.01 | 0/26 (0) | .58 |
| Influenza vaccination history | |||||
| History of vaccination within the previous 12 months | 63/95 (66) | 259/641 (40) | <.01 | 8/26 (31) | .002 |
| LAIV used for most recent vaccination | 38/73 (52) | 96/340 (28) | <.01 | 4/9 (44) | .74 |
| Clinical symptoms | |||||
| Time to presentation, median days (IQR) | 2 (1–3) | 2 (1–4) | .02 | 3 (2–6) | .002 |
| Setting of initial influenza testing | <.01 | .01 | |||
| Outpatient clinic | 33/97 (34) | 320/641 (50) | 17/26 (65) | ||
| Emergency department | 26/97 (27) | 284/641 (44) | 5/26 (29) | ||
| Ship/training Depot | 38/97 (39) | 19/641 (3) | 4/26 (15) | ||
| Hospital ward | 0/97 (0) | 18/641 (3) | 0/26 (0) | ||
| Fever | 91/91 (100) | 465/606 (77) | <.01 | 22/23 (96) | .20 |
| Cough | 87/91 (96) | 449/606 (74) | <.01 | 20/23 (87) | .15 |
| Rhinorrhea | 40/91 (44) | 259/606 (43) | .82 | 18/23 (78) | .005 |
| Myalgia or arthralgia | 52/91 (57) | 223/606 (37) | <.01 | 10/23 (43) | .25 |
| Sore throat | 46/91 (51) | 288/606 (48) | .65 | 17/23 (74) | .06 |
| Eye symptoms | 9/91 (10) | 38/606 (6) | .26 | 1/23 (4) | .68 |
| Nausea | 23/91 (25) | 148/606 (24) | .90 | 6/23 (26) | >.99 |
| Vomiting | 17/91 (19) | 134/606 (22) | .50 | 3/23 (13) | .76 |
| Diarrhea | 6/91 (7) | 117/606 (19) | <.01 | 1/23 (4) | >.99 |
| Headache | 45/91 (49) | 225/606 (37) | .03 | 11/23 (48) | >.99 |
| Temperature | |||||
| Median °F (IQR) | 101.0 (100.2–102.0) | 99.6 (98.2–101.6) | <.01 | 101.0 (98.7–102.1) | .39 |
| ≥38°C | 66/89 (74) | 243/595 (41) | <.01 | 15/24 (63) | .31 |
NOTE. Data are proportion (%) of patients, unless otherwise indicated. COPD, chronic obstructive pulmonary disease; IQR, interquartile range; LAIV, live attenuated influenza vaccine.
a
P value compares H1N1 group to influenza negative group.
b
P value compares H1N1 group to H3/B group.