Incidence estimates of laboratory-confirmed influenza illness in ambulatory care settings among infants under 6 months of age
| First author (year) | Time period | Number of cases | Denominator | Rate per 100 (95% CI) | Adjustment |
| Ali (2016)34 | October 2011 to June 2014 | Three* | 399† | 0.75 per 100 person-years (0.0 to 1.6) | None |
| Budge (2014)37 | May 2009 to September 2011 | –‡ | –‡ | 35 per 100 person-years (26 to 48) | Rate adjusted for clustering at the individual child level due to multiple episodes. |
| Madhi (2014)16 | 2011 to 2012 | 37 | 1023 | 3.6 per 100 population (2.6 to 5.0) | None |
| Poehling (2006)9 | 2002–2003 to 2003–2004§ | –‡ | –‡ | 2002 to 2003: 2.8 per 100 population (0.7 to 11.1) 2003 to 2004: 5.9 per 100 population (2.8 to 12.8) | Rate adjusted by multiplying the influenza burden for each age group and study year by age-specific rate of acute respiratory tract infection or fever estimated from the National Ambulatory Medical Care Survey (NAMCS) and the National Hospital Ambulatory Medical Care Survey (NHAMCS). |
| Tapia (2016)17 | 12 September 2011 to 28 January 2014 | 77 | 927¶ | 8.3 per 100 person-years (6.6 to 10.3)¶ | None |
| Zhang (2016)42 | April 2011 to March 2014 | 420** 487** 252** 1160** | 11 057 12 393 13 674 37 124 | 2011 to 2012: 5.7 per 100 population (3.6 to 8.3) 2012 to 2013: 7.9 per 100 population (2.8 to 14.1) 2013 to 2014: 2.3 per 100 population (1.2 to 3.6) 2011 to 2014: 4.9 per 100 population (2.4 to 7.9) | Adjusted for the age-specific proportion of all influenza-associated ILI outpatient visits at the surveillance hospital. |
*Influenza B only.
†Number of person-years contributed by 692 infants.
‡Not reported in original study and insufficient information to compute.
§Rates based on number of outpatient clinic visits attributable to influenza in 2002–2003 to 2003–2004 only.
¶Number of person-years contributed by 2041 infants. Rate and 95% CI derived by converting person-days to person-years.
**Age-specific numerators estimated by multiplying the number of visits for influenza-like illness (ILI) by the influenza positive proportion of enrolled ILI cases.