Table 2. Demographic and clinical characteristics associated with influenza B lineages, determined by multivariable logistic regression analysis, among influenza B-positive patients hospitalized with severe acute respiratory illness, South Africa, 2009–2014.
| Characteristics of Patients | Influenza B n/Nb (%) | B/Victoria n/Nc (%) |
B/Yamagata n/Nc (%) |
Untyped B n/Nd (%) |
Odd Ratio (95% CI) |
P-value | Adjusted Odd ratio (95% CI) |
P-value |
|---|---|---|---|---|---|---|---|---|
| Yeara | ||||||||
| 2009 | 28/484 (5.8) | 15/181 (8.3) | 4/105 (3.8) | 9/198 (4.5) | Reference | - | Reference | - |
| 2010 | 179/484 (37.0) | 70/181 (38.7) | 4/105 (3.8) | 105/198 (53) | 0.2 (<0.1–0.9) | 0.036 | 0.2 (<0.1–1.1) | 0.057 |
| 2011 | 128/484 (26.4) | 13/181 (7.2) | 62/105 (59.0) | 53/198 (26.8) | 15.9 (4.8–53.1) | <0.001 | 11.8 (3.1–45.7) | <0.001 |
| 2012 | 122/484 (25.2) | 83/181 (45.9) | 16/105 (15.2) | 23/198 (11.6) | 0.7 (0.2–2.2) | 0.521 | 0.5 (0.1–2.0) | 0.327 |
| 2013 | 20/484 (4.1) | 0/181 (0.0) | 16/105 (15.2) | 4/198 (2) | 113.7 (5.6–234.2) | 0.002 | 73.7 (3.3–186.4) | 0.007 |
| 2014 | 7/484 (1.4) | 0/181 (0.0) | 3/105 (2.9) | 4/198 (2) | 24.1 (1.1–53.7) | 0.047 | 9.7 (0.3–17.6) | 0.189 |
| Age (in years) | ||||||||
| 0–4 | 199/482 (41.3) | 87/181 (48.1) | 39/104 (37.5) | 73/197 (37.1) | Reference | - | Reference | - |
| 5–24 | 47/482 (9.8) | 19/181 (10.5) | 11/104 (10.6) | 17/197 (8.6) | 1.3 (0.6–3.0) | 0.547 | 1.6 (0.4–6.5) | 0.526 |
| 25–44 | 146/482 (30.3) | 54/181 (29.8) | 32/104 (30.8) | 60/197 (30.5) | 1.3 (0.7–2.4) | 0.344 | 2.0 (0.6–6.2) | 0.233 |
| 45–64 | 68/482 (14.1) | 18/181 (9.9) | 14/104 (13.5) | 36/197 (18.3) | 1.7 (0.8–3.8) | 0.174 | 4.2 (1.1–16.5) | 0.038 |
| ≥65 | 22/482 (4.6) | 3/181 (1.7) | 8/104 (7.7) | 11/197 (5.6) | 5.9 (1.5–23.6) | 0.011 | 12.2 (2.3–64.4) | 0.003 |
| Sex (Female) | 278/483 (57.6) | 106/181 (58.6) | 63/104 (60.6) | 109/198 (55.1) | 1.1 (0.7–1.8) | 0.739 | ||
| Underlying medical conditions | ||||||||
| Any | 52/483 (10.8) | 24/181 (13.3) | 14/104 (13.5) | 14/198 (7.1) | 1.0 (0.5–2.1) | 0.962 | ||
| Asthma | 16/483 (3.3) | 7/181 (3.9) | 5/104 (4.8) | 4/198 (2) | 1.3 (0.4–4.1) | 0.704 | ||
| Chronic lung disease | 1/483 (0.2) | 1/181 (0.6) | 0/104 (0.0) | 0 | 1.7 (0.0–67.8) | 1.000 | ||
| Chronic heart disease | 2/483 (0.4) | 1/181 (0.6) | 0/104 (0.0) | 1/198 (0.5) | 1.7 (0.0–67.8) | 1.000 | ||
| Diabetes | 11/483 (2.3) | 2/181 (1.1) | 5/104 (4.8) | 4/198 (2) | 4.5 (0.9–23.7) | 0.075 | ||
| Obesity | 3/483 (0.6) | 2/181 (1.1) | 1/104 (1.0) | 0 | 0.9 (0.1–9.7) | 0.909 | ||
| HIV infection | 194/405 (47.9) | 65/145 (44.8) | 34/90 (37.8) | 95/170 (55.9) | 0.7 (0.4–1.3) | 0.288 | 0.4 (0.2–0.9) | 0.047 |
| Duration of symptoms ≥3 (in days) | 273/480 (56.9) | 100/180 (55.6) | 56/104 (53.8) | 117/196 (59.7) | 0.9 (0.6–1.5) | 0.780 | ||
| Duration of hospitalization (in days) | ||||||||
| <3 | 145/470 (30.9) | 59/177 (33.3) | 34/98 (34.7) | 52/195 (26.7) | Reference | |||
| 3–7 | 221/470 (47.0) | 84/177 (47.5) | 48/98 (49.0) | 89/195 (45.6) | 1.0 (0.6–1.7) | 0.976 | ||
| ≥8 | 104/470 (22.1) | 34/177 (19.2) | 16/98 (16.3) | 54/195 (27.7) | 0.8 (0.4–1.7) | 0.586 | ||
| Progression of illness and in-hospital outcome | ||||||||
| Died | 19/475 (4.0) | 5/179 (2.8) | 5/99 (5.1) | 9/197 (4.6) | 1.9 (0.5–6.6) | 0.340 | ||
| ICU admission | 4/475 (0.8) | 3/178 (1.7) | 0/100 (0.0) | 1/197 (0.5) | 0.5 (0.0–4.3) | 0.522 | ||
| Oxygen therapy | 168/475 (35.4) | 59/178 (33.1) | 31/100 (31.0) | 78/197 (39.6) | 0.9 (0.5–1.5) | 0.714 |
a Estimate using penalized logistic regression.
bTotal number of influenza B viruses detected in the SARI cases of which n had the respective data available.
cTotal number of influenza B/Victoria or B/Yamagata viruses detected in SARI cases of which n had the respective data.
dTotal number of untyped influenza B positive cases of which n had the respective data.