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Table 3 Factors associated with influenza infection and tuberculosis-influenza co-infection compared with tuberculosis infection only in patients admitted with severe respiratory illness (acute and chronic) and tested for tuberculosis and influenza at four sites in South Africa, June 2010- December 2011

From: Influenza virus infection is associated with increased risk of death amongst patients hospitalized with confirmed pulmonary tuberculosis in South Africa, 2010–2011

Variables   Laboratory confirmed tuberculosis Referencea Laboratory confirmed influenza Laboratory confirmed tuberculosis-influenza co-infection
n/N (%) RRRb ARRRc(95% CI) n/N (%) RRRb ARRRc(95% CI)
Age group (years) 0-4 47/423 (11) 46/275 (10) Reference Reference 8/34 (22) Reference Reference
5-24 44/423 (10) 28/275 (11) 0.6 (0.3-1.2) 1.3 (0.6-2.9) 3/34 (9) 0.4 (0.1-1.6) 0.5 (0.1-2.5)
  25-44 231/423 (55) 121/275 (44) 0.5 (0.3-0.8) 1.5 (0.8-2.8) 18/34 (53) 0.5 (0.2-1.2) 0.5 (0.2-1.7)
  45-64 86/423 (20) 57/275 (21) 0.7 (0.4-1.1) 1.3 (0.7-2.5) 4/34 (12) 0.3 (0.1-0.9) 0.3 (0.1-2.5)
  65+ 15/423 (3) 23/275 (8) 1.6 (0.7-3.4) 3.9 (1.6-9.8) 1/34 (3) 0.3 (0.04-3.4) 9.53e-07
Sex Female 247/423 (58) 176/275 (64) Reference   20/34 (59) Reference  
  Male 176/176 (42) 99/275 (36) 0.8 (0.6-1.1)   14/34 (41) 1.0 (0.5-1.9)  
Site Chris Hani Baragwanath 124/423 (29) 169/275 (61) Reference   17/34 (50) Reference  
  Mapulaneng & Matikwana 21/423 (5) 11/275 (4) 0.4 (0.2-0.8)   2/34 (6) 0.7 (0.1-3.2)  
  Edendale 48/423 (11) 22/275 (8) 0.3 (0.2-0.6)   1/34 (3) 0.2 (0.01-1.2)  
  Klerksdorp/Tshepong 230/423 (54) 73/275 (27) 0.2 (0.2-0.3)   14/34 (41) 0.4 (0.2-0.9)  
HIV status Negative 82/392 (21) 99/257 (39) Reference Reference 7/32 (22) Reference Reference
Positive 310/392 (79) 158/257 (61 0.4 (0.3-0.6) 0.6 (0.4-0.9) 25/32 (78) 0.9 (0.4-2.3) 1.6 (0.5-4.9)
Underlying medical conditionsd No 394/423 (93) 240/275 (87) Reference   32/34 (94) Reference  
Yes 29/423 (7) 35/275 (13) 1.98 (1.2-3.3)   2/34 (6) 0.8 (0.2-3.7)  
Duration of symptoms prior to admission <7 166/412 (40) 194/275 (71) Reference Reference 24/33 (73) Reference Reference
≥7 246/412 (60) 81/275 (29) 0.3 (0.2-0.4) 0.4 (0.2-0.4) 9/33 (27) 0.3 (0.1-0.6) 0.3 (0.1-0.7)
Pneumoccocal co-infection on PCRe No 371/388 (96) 233/246 (95) Reference Reference 29/30 (97)   
Yes 17/388 (4) 13/246 (5) 1.2 (0.6-2.6)   1/30 (3) 0.8 (0.1-5.8)  
Oxygen therapy No 313/423 (74) 158/275 (57) Reference Reference 24/34 (71) Reference Reference
  Yes 110/423 (26) 117/275 (43) 2.1 (1.5-2.9) 1.9 (1.3-2.8) 10/34 (29) 1.2 (0.5-2.6) 0.97 (0.4-2.3)
Tuberculosis treatment No 185/422 (44) 243/274 (89) Reference   20/34 (59) Reference  
Yes 237/422 (56) 31/274 (11) 0.1 (0.1-0.2)   14/34 (41) 0.5 (0.3-1.1)  
Hospital duration (days) 257/420 (61) 198/274 (72) Reference   22/33 (67) Reference Reference
>7 163/420 (39) 76/274 (28) 0.6 (0.4-0.8) 0.6 (0.4-0.9) 11/33 (33) 0.8 (0.4-1.7) 0.7 (0.3-1.5)
Died No 391/422 (73) 265/274 Reference Reference 30/34 (88) Reference Reference
  Yes 31/422 (7) 9/274 0.4 (0.2-0.9) 0.5 (0.2-1.1) 4/34 (12) 1.7 (0.6-5.1) 3.2 (1.1-10.0)
  1. aTuberculosis only group used as reference for multinomial model analysis (i.e. comparing influenza only to tuberculosis only and tuberculosis–influenza co-infection to tuberculosis only group).
  2. bUnadjusted relative risk ratio (RRR) at multivariable analysis.
  3. cAdjusted relative risk ratio (ARRR) at multivariable analysis.
  4. dUnderlying conditions included any of the following: Asthma, other chronic lung disease, chronic heart disease (valvular heart disease, coronary artery disease, or heart failure excluding hypertension), liver disease (cirrhosis or liver failure), renal disease (nephrotic syndrome, chronic renal failure), diabetes mellitus, immunocompromising conditions excluding HIV infection (organ transplant, immunosuppressive therapy, immunoglobulindeficiency, malignancy), neurological disease (cerebrovascular accident, spinal cord injury, seizures, neuromuscular conditions) or pregnancy. Comorbidities were considered absent in cases for which the medical records stated that the patient had no underlying medical condition or when there was no direct reference to that condition.
  5. elyt A PCR positive for Streptococcus pneumoniae on blood specimen.