Table 3.
Observed and estimated relative risk of S. pneumoniae (Sp) carriage, according to S. aureus (Sa) status, and influenza or other virus exposure. Departures from additivity on the risk scale indicate biological interaction between Sa carriage and viral infection in terms of Sp carriage
| Observed | Estimated additive effect | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Neither (ref.) | Sa carriage | Virus detected | Both | |||||||
| Sp+/total | RR | Sp+/total | RR (95% CI) | Sp+/total | RR (95% CI) | Sp+/total | RR (95% CI) | RR | RERI (95% CI)† | |
| Influenza | ||||||||||
| Children | 61/139 | 1·00 | 19/32 | 1·35 (0·96–1·91) | 6/11 | 1·47 (1·01–2·14) | 2/4 | 1·14 (0·42–3·09) | 1·60 | −0·11 (−1·55 to 1·33) |
| Adults | 24/119 | 1·00 | 4/15 | 1·32 (0·53–3·29) | 3/16 | 1·15 (0·38–3·44) | 1/2 | 2·48 (0·59–10·37) | 1·25 | 1·49 (−2·25 to 5·25) |
| All ages | 85/258 | 1·00 | 23/47 | 1·49 (1·06–2·09) | 9/27 | 1·28 (0·84–1·96) | 3/6 | 1·52 (0·67–3·44) | 1·50 | −0·65 (−2·04 to 0·74) |
| Any virus* | ||||||||||
| Children | 14/43 | 1·00 | 4/7 | 1·76 (0·81–3·80) | 52/107 | 1·31 (0·99–1·75) | 17/29 | 1·80 (1·06–3·05) | 2·28 | −0·27 (−1·43 to 0·89) |
| Adults | 8/51 | 1·00 | 4/12 | 1·28 (0·20–8·23) | 19/85 | 1·28 (0·70–2·33) | 1/5 | 2·13 (0·76–5·91) | 1·70 | 0·04 (−2·88 to 2·95) |
| All ages | 22/94 | 1·00 | 21/41 | 1·78 (0·83–3·82) | 72/192 | 1·38 (1·06–1·79) | 5/12 | 2·19 (1·36–3·51) | 2·38 | −0·23 (−1·51 to 1·04) |
Sp+, Subjects carrying S. pneumoniae; RR, relative risk; CI, confidence interval; RERI, relative excess risk due to interaction.
Any virus includes all 13 virus tested for (influenza A/B, adenovirus; coronaviruses 229E, HKU1, NL63, and OC43; human metapneumovirus, parainfluenza 1, 2, 3; rhinovirus; respiratory syncytial virus).
The RERI estimates departures from additivity on the relative risk scale. A negative value implies antagonism, the null value is 0. RERI measures antagonism between virus detection (influenza or any virus) and Sa carriage in regards to Sp carriage and not antagonism between Sa and Sp.