Table 1. Study characteristics.
| First author, Year | Time period | Region of conduct | Data source(s) | Number of lab-confirmed H1N1 [confirmation type] | Outcome(s) examined |
| ETHNIC MINORITIES | |||||
| Oluyomi-Obi 2010 [19] | March 1–August 31 2009 | Manitoba, Canada | St. Boniface Hospital & Health Sciences Centre ICU | 889 [PCR] | ICU admission |
| CDC Sept 2009 [20] | April-August 8 2009 | US | CDC influenza-associated pediatric mortality reporting system | 36 pediatric deaths [RT-PCR] | Mortality |
| Martin 2010 [21] | April 1–October 31 2009 | North Carolina, US | Duke University Medical Center | 123 hospitalizations [RT-PCR, viral culture] | Hospitalization |
| Paine 2010 [22]*(1) | April 1–November 1 2009 | New Zealand | EpiSurv | 3067 [PCR, viral culture, antibody assay] | Mortality |
| Baker 2009 [23] (1) | April 25–August 23 2009 | New Zealand | Surveillance data from notifiable disease, general practices, laboratories, Healthline, Ministry of Health ICU, population survey (Flutracker) | 3109 [PCR, viral culture, antibody assay] | Hospitalization |
| Wenger 2011 [24] | April 1– December 31 2009 | Alaska, US | Alaska ILI Surveillance Network, Medicaid, Indian Health Service Influenza Awareness System | 103 hospitalizations [PCR, viral culture] | Hospitalization, mortality |
| Zarychanski 2010 [25] | April 2–September 5 2009 | Manitoba, Canada | Manitoba Health and University of Manitoba Critical Care | 894 (location known for 795) [RT-PCR] | Hospitalization, ICU admission |
| Helferty 2010 [26]*(2) | April 12 2009– April 3 2010 | Canada | PHAC | 8678 hospitalizations [RT-PCR, viral culture, antibody assay] | Hospitalization, ICU admission, mortality |
| Campbell 2010 [27] (2) | April 26–September 26 2009 | Canada | PHAC | 1479 hospitalizations [RT-PCR, viral culture, antibody assay] | Hospitalization, ICU admission, mortality |
| Siston 2010 [28] | April 14 -August 21 2009 | US | CDC (Pregnancy Flu Line) | 788 pregnant women [rRT-PCR, antibody assay, rapid test, viral culture] | Hospitalization, ICU admission, mortality |
| CDC Dec 2009 [29] | April 15–November 13 2009 | US | Multidisciplinary workgroup from 12 state health departments | NR [rapid test, antibody assay, rRT-PCR, viral culture] | Mortality |
| Chitnis 2010 [30]*(3) | April 23–August 15 2009 | Wisconsin, US | Wisconsin Division of Public Health | 252 hospitalizations [rRT-PCR] | Hospitalization, ICU admission, mortality |
| Truelove 2011 [31] (3) | April 15 2009–January 2 2010 | Wisconsin, US | Wisconsin Division of Public Health | 1266 [rRT-PCR] | Hospitalization, mortality |
| Dee 2011 [32] | April 15 2009–January 26 2010 hospitalization (pediatric deaths: April 15 2009– March 23 2010) | US | Emerging Infections Program (CDC, 10 state and local health departments, academic institutions, medical providers), CDC Influenza-Associated Pediatric Mortality Surveillance System | 5793 hospitalizations [rapid test, RT-PCR, viral culture, documented in medical chart] | Hospitalization, mortality |
| Jung 2011 [33] *(4) unpublished data | April 16 2009–April 12 2010 | Canada | Canadian Critical Care Trials Group | 565 critically ill [rRT-PCR, viral culture] | ICU admission |
| Jouvet 2010 [34] (4) | April 16–August 15 2009 | Canada | Canadian Critical Care Trials Group | 49 pediatric ICU admissions [PCR, viral culture] | Pediatric ICU admission |
| Louie 2011 [35]*(5) unpublished data | April 1 2009–August 13 2010 | California, US | California Department of Public Health | 2476 hospitalizations [rRT-PCR] | Hospitalization, ICU admission, mortality |
| CDC May 2009 [36] (5) | April 20–May 17 2009 | California, US | California Department of Public Health | 333 hospitalizations [rRT-PCR] | Hospitalization |
| Lee 2010 [37] | April 24–July 1 2009 | New York City, US | New York City Department of Health and Mental Hygiene, New York City Office of Vital Statistics (death certificates) | 47 deaths [rRT-PCR] | Mortality |
| CDC Aug 2009 [38] | April 24–July 25 2009 | Illinois, US | Chicago Department of Public Health | 1557 [rRT-PCR] | Hospitalization |
| CDC Jan 2010 [39] | April 25–May 24 2009 | New York City, US | New York City Department of Health and Mental Hygiene (all hospitals) | 99 hospitalizations [PCR] | Hospitalization |
| Kwan-Gett 2009 [40] | April 25–August 7 2009 | Washington, US | Public Health–Seattle & King County | 565 [viral culture, PCR] | Mortality |
| Nguyen-Van-Tam 2010 [41] | April 27–Sept 30 2009 | UK | The Influenza Clinical Information Network (FluCAN) | 631 hospitalizations [rRT-PCR] | Hospitalization |
| Kumar 2010 [42] | April 28–August 31 2009 | Wisconsin, US | Children’s Hospital of Wisconsin | 81 hospitalizations [rRT-PCR] | Hospitalization, mortality |
| Harris 2010 [43] | April-August 2009 | Queensland, Australia | Townsville Hospital | 360 [rPCR] | Hospitalization, ICU admission, mortality |
| Kelly 2009 [44] | May-October 2009 | Australia | Australian Department of Health and Ageing | NR [lab-confirmed] | Hospitalization, ICU admission, mortality |
| Jain 2009 [45] | May 1–June 9 2009 | US | State health departments reports to the CDC | 272 hospitalizations [rRT-PCR] | Hospitalization |
| Creanga 2010 [46] | May 1–June 30 2009 | New York, US | New York City Department of Health and Mental Hygiene | 136 hospitalizations [rRT-PCR] | Hospitalization |
| Bettinger 2010 [47] | May 1–August 31 2009 | Canada | The Canadian Immunization Monitoring Program, Active (IMPACT) surveillance data | 324 hospitalizations [PCR, antibody assay, viral culture] | Hospitalization |
| Miller 2010 [48] | May 19–June 30 2009 | Utah, US | Four ICUs at three academic hospitals in Salt Lake County | 47 ICU admissions [PCR] | ICU admission |
| Flint 2010 [49]*(6) | June 1–August 31 2009 | Northern Territory, Australia | Northern Territory CDC, Royal Darwin Hospital | 161 acute care [PCR] | Hospitalization, ICU admission |
| Flint 2009 [50] (6) | May 29– June 18 2009 | Northern Territory, Australia | Northern Territory CDC, Royal Darwin Hospital | 81 [PCR] | Hospitalization |
| Cretikos 2009 [51] | May 15– September 4 2009 | New South Wales, Australia | NetEpi, laboratory notifications, hospital emergency department and ambulance dispatch surveillance system, death certificate surveillance | 5106 [PCR] | Hospitalization, ICU admission, mortality |
| Scriven 2009 [52] | June 1–July 21 2009 | Birmingham, UK | Heartlands Hospital | 3000 [PCR] | Hospitalization, severe illness |
| Webb 2009 [53]*(7) | June 1–August 31 2009 | New Zealand, Australia | Australian and New Zealand Intensive Care Research Centre | 722 ICU admissions [PCR, serology] | ICU admission |
| Knight 2010 [54] (7) | June 1–August 31 2009 | Australia, New Zealand | Australian and New Zealand Intensive Care Research Centre, Australasian Maternity Outcomes Surveillance System | 59 ICU pregnancy admissions [confirmed H1N1] | ICU admission |
| ANZIC Investigators 2010 [55] (7) | June 1–August 31 2009 | New Zealand, Australia | Australian and New Zealand Intensive Care Research Centre, Australasian Maternity Outcomes Surveillance System | 64 ICU pregnancy/postpartum admissions [PCR] | ICU admission |
| Verrall 2010 [56] *(8) | June 8–August 31 2009 | Wellington, New Zealand | Wellington Hospital and Hutt Valley Hospitals | 229 hospitalizations [rRT-PCR] | Hospitalization |
| Dee 2010 [57] (8) | June 17–July 20 2009 | Wellington, New Zealand | Hutt Valley Hospital | 54 hospitalizations [RT-PCR] | Hospitalization |
| Sachedina 2010 [58] | June 26 2009– March 22 2010 | England, UK | Department of Health, Regional Directors of Public Health, Health Protection Agency’s influenza reference centers | 70 deaths [lab-confirmed or H1N1 on death certificate] | Mortality |
| Kelly 2011 [59] | July 1–December 4 2009 | Australia | Influenza Complications Alert Network (FluCAN) sentinel hospitals | 465 hospitalizations [rRT-PCR] | Hospitalization, ICU admission |
| Chien 2010 [60] | July 2–August 29 2009 | Taiwan, Republic of China | Taiwan CDC | 149 severe illness[RT-PCR] | Pneumonia, respiratory failure |
| Subramony 2010 [61] | July 15–September 28 2009 | Singapore | Singapore General Hospital, Tan Tock Seng Hospital, Alexandra Hospital, National University Hospital, KK Women’s and Children’s Hospital and Changi General Hospital, Mount Elizabeth Hospital, Gleneagles Hospital, Mount Alvernia Hospital, East Shore Hospital, Thompson Medical Centre and Raffles Hospital | 1348 hospitalizations [RT-PCR] | Hospitalization, severe illness |
| Satterwhite 2010 [62] | August 1–October 31 2009 | Atlanta, Georgia, US | Emory University Hospital, Grady Memorial Hospital, Emory University Hospital Midtown/Crawford Long Hospital, Atlanta Veterans Affairs Medical Center | 109 hospitalizations [PCR] | Hospitalization, ICU admission |
| Bandaranayake 2011 [63] | January 1–Oct 24 2010 | New Zealand | Institute of Environmental Science and Research, Healthstat, Healthline, Episurv, National Minimum Data Set, Pandemic Influenza Mortality Review Committee | 1758 [nasopharyngeal swabs] | Hospitalization |
| LOW-INCOME ECONOMIES OR LOWER-MIDDLE-INCOME ECONOMIES | |||||
| Reyes 2010 [64] | May-December 2009 | Guatemala | National Hospital of Cuilapa, Western Regional Hospital, Health Center of Nueva Santa Rosa | 239 [rRT-PCR] | Hospitalization, ICU admission, pneumonia, mechanical ventilation, mortality |
| Louriz 2010 [65] | June-December 2009 | Rabat, Morocco | Ibn Sina University Hospital | 186 hospitalizations [RT-PCR] | Hospitalization, ICU admission, mechanical ventilation, mortality |
| Lahlou 2011 [66] | June 12–December 24 2009 | Rabat, Morocco | Mohammed V Military Teaching Hospital | 240 [rRT-PCR] | Hospitalization, severe illness, mortality |
| Jagannatha Rao 2011 [67] | August 2009–April 2010 | Karnataka, India | Tertiary care hospital | 20 hospitalizations [rRT-PCR] | Hospitalization, severe illness, mortality |
| Chacko 2010 [68] | August-October 2009 | Karnataka, India | Manipal Hospital multidisciplinary ICU | 66 hospitalizations [RT-PCR] | Hospitalization, ICU admission, mortality |
| Parakh 2010 [69] | August 2009–January 2010 | New Delhi, India | Kalawati Saran Children’s Hospital | 25 pediatric hospitalizations [PCR] | Hospitalization, ICU admission, severe illness, mortality |
| Ramakrishna 2011 [70]*(9) | August 2009–October 2010 | Tamil Nadu, India | Christian Medical College Hospital | 629 hospitalizations [rRT-PCR] | Hospitalization, ICU admission, severe illness mortality |
| Pramanick 2011 [71] (9) | August 5 2009–January 2010 | Tamil Nadu, India | Christian Medical College Hospital | 164 [rRT-PCR] | Hospitalization, ICU admission, mortality |
| Puvanalingam 2011 [72] | August 9 2009–January 2010 | Tamil Nadu, India | Madras Medical College and Government General Hospital records, Institute of Child Health, Egmore | 442 [RT-PCR] | Hospitalization, pneumonia, mortality |
| Sharma 2010 [73] | September 2009 to January 2010 | Delhi, India | GTB Hospital | 125 hospitalizations [RT-PCR] | Hospitalization, severe illness, mortality |
| Chudasama 2011 [74]* (10) | September 1, 2009–February 20, 2010 | Gujarat, India | Hospitals in Rajkot city of Saurashtra region | 274 hospitalizations [rRT-PCR] | Hospitalization, mortality |
| Chudasama 2010 [75] (10) | September 1, 2009–February 28, 2010 | Rajkot, India | Hospital records, Pediatric Department of Civil Hospital & two other pediatric hospitals of Rajkot city | 62 pediatric cases [rRT-PCR] | Hospitalization, mortality |
| Chudasama 2010 [76] (10) | September 1, 2009–February 20, 2010 | Rajkot, India | Hospitals in Rajkot city of Saurashtra region | 274 hospitalizations [rRT-PCR] | Hospitalization, mortality |
| Chudasama 2010 [77] (10) | September 1, 2009–February 20, 2010 | Rajkot, India | Hospitals in Rajkot city of Saurashtra region | 274 hospitalizations [rRT-PCR] | Hospitalization, mortality |
| Chudasama 2010 [78] (10) | September 1, 2009–January 31, 2010 | Rajkot, India | Hospitals in Rajkot city of Saurashtra region | 274 hospitalizations [rRT-PCR] | Hospitalization, mortality |
| Gupta 2011 [79] | November 2009–February 2010 | Rajasthan, India | Umaid Hospital for Women and Children | 62 pediatric hospitalizations [rPCR] | Hospitalization, ICU admission, mortality |
| Naseem 2011 [80] | December 1 2009–May 30 2010 | Rawalpindi, Pakistan | Department of Pulmonology and Critical Care, Military Hospital | 36 hospitalizations [RT-PCR] | Hospitalization, ICU admission, mechanical ventilation, mortality |
Notes: *major publication, () denotes companion reports.
Abbreviations: CDC Centers for Disease Control, ICU intensive care unit, ILI influenza-like illness, NR not reported, PCR polymerase chain reaction, rRT-PCR real-time reverse transcription-PCR, PH public health, PHAC Public Health Agency of Canada, SES socioeconomic status, UK United Kingdom.