Table 2. Bivariate association between influenza-associated respiratory hospitalization rates and predictive covariates among 16 countries in the Americas participating in the analysis, 2010–2015.
| <5 years | 5–64 years | ≥65 years | ||||
|---|---|---|---|---|---|---|
| Rate ratio * (95% CI) |
P-value † | Rate ratio * (95% CI) |
P-value † | Rate ratio * (95% CI) |
P-value † | |
| Country | — | <0·001 | — | <0·001 | — | <0·001 |
| Year ‡ | 0·002 | <0·001 | 0·025 | |||
| 2010 | Reference | Reference | Ref Reference | |||
| 2011 | 0·4 (0·3, 0·7) | 0·5 (0·4, 0·7) | 0·6 (0·4, 1·0) | |||
| 2012 | 0·7 (0·5, 1·0) | 0·8 (0·6, 1·1) | 0·8 (0·6, 1·2) | |||
| 2013 | 0·6 (0·4, 0·9) | 0·9 (0·7, 1·2) | 0·9 (0·6, 1·4) | |||
| 2014 | 0·5 (0·3, 0·7) | 0·6 (0·5, 0·9) | 1·1 (0·7, 1·7) | |||
| 2015 | 0·6 (0·3, 1·0) | 0·7 (0·5, 1·1) | 1·3 (0·8, 2·2) | |||
| WHO influenza transmission zone | 0·96 | 0·21 | 0·07 | |||
| North America | Reference | Reference | Reference | |||
| Central American Caribbean | 0·8 (0·2, 3·1) | 0·4 (0·1, 1·7) | 0·2 (0·1, 0·7) | |||
| Tropical South America | 1·1 (0·2, 4·6) | 1·1 (0·3, 4·5) | 0·4 (0·1, 1·2) | |||
| Temperate South America | 1·0 (0·2, 4·2) | 1·2 (0·3, 4·9) | 0.4 (0.1, 1·4) | |||
| Predominant virus § | 0·06 | <0·001 | 0·31 | |||
| A/H3 viruses | Reference | Reference | Reference | |||
| A/H1 viruses | 1·6 (1·1, 2·2) | 1·7 (1.4, 2.2) | 1·1 (0·8, 1·5) | |||
| B viruses | 1·2 (0·7, 1·9) | 1·2 (0·8, 1·6) | 0·7 (0·4, 1·1) | |||
| Mixed | 1·4 (0·9, 2·3) | 1·3 (0·9, 1·8) | 1·1 (0·7, 1·7) | |||
| World Bank income category | 0·19 | 0·31 | 0·06 | |||
| Low-middle/Low | Reference | Reference | Reference | |||
| Upper-middle | 0·4 (0·2, 1·1) | 0·8 (0·2, 2·4) | 0·7 (0·3, 2·0) | |||
| High | 0·7 (0·2, 2·0) | 1·6 (0·5, 5·8) | 1·9 (0·6, 5·8) | |||
| Density of hospital beds, per 10,000 (in quartiles) | 0·08 | 0·43 | <0·001 | |||
| <1·5 | Reference | Reference | Reference | |||
| 1·5–2·2 | 3·6 (1·2, 11·3) | 3·2 (0·7, 13·8) | 6·5 (2·7, 16·1) | |||
| 2·3–3·7 | 3·6 (1·1, 12·0) | 3·0 (0·7, 13·8) | 2·6 (1·1, 6·7) | |||
| ≥3·8 | 4.3 (1·4, 13·4) | 2·1 (0·5, 9·1) | 2·5 (1·0, 6·3) | |||
* Rate ratios were estimated from a bivariate random effects meta-regression of log-transformed rates of influenza-associated hospitalization and the specified covariate; the rate ratios compare the rate in the category to the reference. A rate ratio is provided because rates were log-transformed prior to analysis in the meta-regression.
† P-values from an omnibus test of association between the log-transformed rate of influenza-associated hospitalization and the specified covariate in a bivariate random effects meta-regression.
‡ For countries in the North American influenza transmission zone, year of observation was defined from July of the labeled year to June of the subsequent year. For all other countries, year of observation was defined from January to December. Eleven countries contributed data for 2010, 14 countries contributed data for 2011, 15 countries contributed data for 2012, 16 countries contributed data for 2013, 12 countries contributed data for 2014, and 6 countries contributed data for 2015.
§ Predominant virus was determined based on the influenza virus type/subtype was comprised ≥40% of the annual influenza-positive specimens submitted to national virologic surveillance. Mixed predominance occurred when no single virus type/subtype comprised ≥40% of specimens.