Table 2. AF and AF-adjusted prevalence of influenza viruses among participants in a study of the AF of influenza virus detection to mild and severe respiratory illnesses, Klerksdorp and Pietermaritzburg, South Africa, May 2012–April 2016*.
| Category |
Total |
|
HIV-infected |
|
HIV-uninfected |
|||
| AF, % (95% CI) |
AF-adjusted prev, % |
AF, % (95% CI) |
AF-adjusted prev, % |
AF, % (95% CI) |
AF-adjusted prev, % |
|||
| Outpatients with influenza-like illness | ||||||||
| Age, y† | ||||||||
| <1 | 96.8 (85.3–99.3) | 7.4 | 98.4 (83.0–∞)‡ | 35.8 | 94.1 (74.9–98.6) | 6.6 | ||
| 1–4 | 92.8 (82.2–97.0) | 14.5 | 94.6 (72.2–98.9) | 19.7 | 90.3 (77.7–95.8) | 14.0 | ||
| 5–24 | 91.4 (81.3–96.0) | 14.8 | 93.5 (77.5–98.1) | 9.8 | 89.8 (78.8–95.1) | 15.6 | ||
| 25–44 | 90.8 (82.7–95.1) | 12.2 | 95.5 (81.8–98.9) | 13.7 | 87.7 (60.2–96.2) | 10.5 | ||
| 45–64 | 93.4 (81.6–97.6) | 12.2 | 95.1 (78.8–98.8) | 16.3 | 91.3 (62.8–98.0) | 9.5 | ||
| >65 | 94.3 (53.2–99.3) | 9.8 | 96.3 (21.1–∞)‡ | 11.1 | 91.8 (27.6–99.1) | 9.2 | ||
| <5 | 93.9 (87.8–97.0) | 12.0 | 97.3 (87.8–99.4) | 25.0 | 91.7 (82.9–96.0) | 11.5 | ||
| >5 | 92.5 (88.2–95.2) | 13.3 | 95.4 (88.5–97.5) | 13.4 | 89.8 (82.4–94.1) | 13.2 | ||
| All | 92.6 (89.3–94.8) | 12.9 | 95.6 (91.0–97.8) | 13.7 | 90.6 (85.5–93.9) | 12.4 | ||
| Influenza virus types/subtypes§ | ||||||||
| A¶ | 93.3 (89.5–95.7) | 8.6 | 96.5 (91.4–98.6) | 9.4 | 91.5 (85.7–95.0) | 8.3 | ||
| A(H3N2) | 97.3 (93.9–98.8) | 6.3 | 98.6 (93.9–99.7) | 7.2 | 96.7 (91.0–98.8) | 6.0 | ||
| A(H1N1)pdm09 | 85.4 (73.1–92.0) | 2.1 | 91.0 (64.9–97.7) | 1.7 | 82.9 (65.7–91.5) | 2.2 | ||
| B |
92.7 (86.5–96.0) |
4.3 |
|
94.4 (82.9–98.2) |
4.3 |
|
91.6 (82.0–96.1) |
4.3 |
| Inpatients with severe acute respiratory illness | ||||||||
| Age (in years)† | ||||||||
| <1 | 93.5 (72.8–98.5) | 4.0 | 94.3 (11.2–∞)‡ | 5.8 | 93.2 (71.2–98.4) | 3.8 | ||
| 1–4 | 87.9 (73.7–94.5) | 7.5 | 90.2 (61.0–97.6) | 10.2 | 86.5 (66.4–94.6) | 6.9 | ||
| 5–24 | 84.3 (59.5–93.9) | 6.6 | 90.6 (64.6–97.5) | 7.2 | 78.6 (13.6–95.9) | 5.9 | ||
| 25–44 | 83.1 (63.3–92.3) | 6.4 | 90.4 (60.1–97.7) | 6.7 | 75.6 (31.8–91.3) | 4.1 | ||
| 45–64 | 87.3 (63.2–95.6) | 6.9 | 90.9 (54–9-97.7) | 8.2 | 85.2 (29.0–96.9) | 5.1 | ||
| >65 | 94.5 (57.7–99.3) | 8.2 | 91.5 (18.6–∞)‡ | 13.5 | 91.0 (27.9–98.9) | 6.5 | ||
| <5 | 89.3 (79.3–94.5) | 5.3 | 91.0 (65.4–97.7) | 7.7 | 89.1 (76.8–94.9) | 5.0 | ||
| >5 | 86.0 (76.9–91.5) | 6.5 | 91.2 (80.3–96.1) | 7.4 | 79.3 (59.6–89.4) | 5.2 | ||
| All | 87.4 (81.3–91.5) | 5.9 | 91.1 (82.2–95.5) | 7.4 | 84.5 (74.7–90.5) | 4.9 | ||
| Influenza virus types/subtypes§ | ||||||||
| A¶ | 86.7 (78.7–91.7) | 3.9 | 91.3 (79.2–96.3) | 4.7 | 81.9 (68.0–89.8) | 3.4 | ||
| A(H3N2) | 93.6 (85.1–97.2) | 2.4 | 94.6 (76.9–98.7) | 2.7 | 92.1 (77.6–97.2) | 2.2 | ||
| A(H1N1)pdm09 | 80.7 (63.5–89.8) | 1.5 | 88.1 (68.7–97.4) | 1.9 | 71.7 (39.2–86.8) | 1.1 | ||
| B |
88.4 (77.6–94.0) |
1.9 |
|
90.3 (71.5–96.7) |
2.7 |
|
89.0 (74.2–95.3) |
1.4 |
| Inpatients with severe chronic respiratory illness | ||||||||
| Age, y† | ||||||||
| <1 | 87.6 (70.7–99.4) | 8.0 | 89. 3(9.3–∞)‡ | 8.9 | 88.1 (72.4–99.8) | 7.8 | ||
| 1–4 | 85.2 (64.8–97.3) | 11.1 | 88.3 (7.4–99.3) | 5.6 | 83.9 (50.9–97.5) | 13.3 | ||
| 5–24 | 81.3 (54.9–92.2) | 6.0 | 85.3 (27.4–95.7) | 5.5 | 78.8 (31.3–93.5) | 7.7 | ||
| 25–44 | 78.7 (43.8–91.9) | 3.8 | 84.6 (35.7–96.3) | 4.1 | 69.5 (32.7–93.0) | 3.8 | ||
| 45–64 | 82.9 (51.1–94.0) | 4.6 | 83.1 (17.6–95.6) | 4.2 | 81.6 (31.5–96.5) | 5.5 | ||
| >65 | 88.2 (38.4–99.0) | 6.4 | 89.7 (12.0–∞)‡ | 6.0 | 88.0 (11.7–98.7) | 6.7 | ||
| <5 | 87.1 (73.0–97.4) | 9.1 | 88.6 (52.4–99.0) | 7.4 | 85.1 (71.7–98.1) | 9.4 | ||
| >5 | 82.7 (70.7–89.8) | 4.5 | 86.9 (64.8–93.2) | 4.3 | 80.2 (60.1–90.2) | 5.7 | ||
| All | 86.2 (77.7–91.5) | 5.0 | 87.4 (69.9–93.7) | 4.5 | 82.9 (74.1–92.3) | 6.5 | ||
| Influenza virus types/subtypes§ | ||||||||
| A¶ | 82.7 (68.6–90.5) | 2.9 | 83.3 (55.8–93.7) | 2.7 | 81.1 (60.5–91.0) | 3.5 | ||
| A(H3N2) | 93.1 (81.3–97.4) | 2.1 | 94.8 (64.1–98.6) | 1.9 | 92.7 (75.5–97.8) | 2.7 | ||
| A(H1N1)pdm09 | 64.5 (32.6–84.6) | 0.7 | 74.2 (17.3–93.8) | 0.8 | 52.8 (9.7–84.5) | 0.6 | ||
| B | 91.5 (82.1–95.9) | 2.2 | 92.4 (80.7–97.0) | 1.8 | 88.9 (61.9–96.8) | 3.2 | ||
*AF, attributable fraction; AF-adjusted prev, prevalence attributable to illness. †The overall influenza virus AF was obtained from models adjusted for any underlying medical conditions and for other respiratory viruses investigated in this study. Underlying medical conditions were asplenia, including asplenia or sickle cell anemia; chronic illness, including chronic lung, renal, liver, or cardiac disease, diabetes mellitus, and asthma; other immunocompromising conditions (excluding HIV), including organ transplant, primary immunodeficiency, immunotherapy, and malignancy; neurologic disorders; burns; obesity; malnutrition; and prematurity. Comorbidities were considered absent in cases for which the medical records stated that the patient had no underlying medical conditions or when there was no direct reference to that condition. Prematurity and malnutrition were assessed only in analyses for children <1 and <5 years of age, respectively. Age and HIV infection were also included as predictors in nonstratified models. ‡Estimated using exact logistic regression. ‡The influenza virus AF was obtained from models adjusted for age, HIV infection, any underlying medical conditions, and other respiratory viruses investigated in this study, including co-circulating influenza virus types and subtypes. ¶Includes influenza A viruses that were not subtyped.