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Table 1 Summary of studies identified in systematic literature review of Incidence of influenza virus infection among pregnant women

From: Incidence of influenza virus infection among pregnant women: a systematic review

Study Outcome assesseda Pandemic or seasonal Study Design Methodology Denominator calculation Dates of surveillance Lab Test Country (WHO Region) b Country Income Level
Creanga 2010 HA, ICU, D Pandemic Case series Retrospective chart review: pregnant women hospitalized with confirmed H1N1 identified through “enhanced surveillance.” Testing performance only when requested by hospital. Estimation using 2007 vital registration data (similar approach as in Jamieson et al.) 05/01/2009–06/30/2009 RT-PCR US (PAHO) High
Doyle 2013 SI, HA, ICU, D Pandemic Case series Cases of pH1N1-confirmed acute respiratory illness reported by health providers to state of Florida Florida birth registry data 04/24/2009–05/31/2010 RT-PCR or viral culture US (PAHO) High
Griffiths 1980 I Seasonal Cohort Serological testing of women “booked” for antenatal care at one hospital in England during three years. Only women with postpartum specimens available were included. Number of study participants 05/1975–11/1975;
HI serology with 4-fold rise in antibody titer UK (EURO) High
Hardy 1961 I Pandemic Cohort All pregnant women treated at Johns Hopkins Obstetrical Prenatal Clinic, with blood samples taken and questionnaires about symptoms administered monthly through delivery. Anyone with high HI titer was considered a case. Number of study participants 10/14/1957–02/01/1958 Complement Complement fixation or HI test; no increase in titers required to be considered a case US (PAHO) High
Irving 2000 I Seasonal Cohort Women delivering at two hospitals in Nottingham, England with available antenatal and postnatal sera. Number of study participants 05/1993–07/1994 Single radial hemolysis and paired specimens for HI titer UK (EURO) High
Jamieson 2009 SI, HA, ICU, D Pandemic Case series Pregnant women with confirmed or probable H1 infection reported by states to CDC as part of “enhanced” surveillance. US Census bureau data 04/15/2009–05/18/2009 Confirmed: RT-PCR or viral culture+for H1. Probable: RT-PCR flu A+ but (−) for known subtypes US (PAHO) High
Knight 2011 ICU, D Pandemic Case series Cases of H1 lab-confirmed ICU admission among pregnant women in Australia and New Zealand reported to Australian and New Zealand Intensive Care (ANZIC) study. Cases in UK reported to UK Obstetric Surveillance System. National statistics on pregnancies combined with total birth data AUS/NZ:
Not stated in manuscript (but referenced) Australia and New Zealand (WPRO)
Madhi 2014 SI Seasonal Randomized Clinical trial RCT of influenza vaccine efficacy. All participants with ILI or unknown respiratory illness were tested for influenza. All women enrolled in placebo arm of study 03/2011–08/2011;
RT-PCR South Africa (AFRO) Upper-Middle
Yates 2010c HA, ICU, D Pandemic Case series Clinician-reported of H1-confirmed pregnant women admitted to 221/223 hospitals with consultant-led maternity units in the UK. Surveillance included zero-reporting and follow-up of reported cases. Birth data from UK office for national statistics 09/01/2009–01/31/2010 Not specified UK (EURO) High
  1. aOutcomes are abbreviated as follows: I Infection, SI Symptomatic Infection, HA Hospital admission, ICU ICU admission, D Death
  2. bWHO regions are abbreviated as follows: PAHO Americas, EURO Europe, AFRO Africa, WPRO Western Pacific
  3. cThe Yates study described same population as described in Knight study; therefore only Knight study results were included in the ICU and death tables