title: Epidemiology and virology of acute respiratory infections during the first year of life: a birth cohort study in Vietnam.
abstract: BACKGROUND
  Understanding viral etiology and age-specific incidence of acute respiratory infections in infants can help identify risk groups and inform vaccine delivery, but community-based data is lacking from tropical settings.
  
  
  METHODS
  One thousand four hundred and seventy-eight infants in urban Ho Chi Minh City and 981 infants in a semi-rural district in southern Vietnam were enrolled at birth and followed to 1 year of age. Acute respiratory infection (ARI) episodes were identified through clinic-based illness surveillance, hospital admissions and self-reports. Nasopharyngeal swabs were collected from infants with respiratory symptoms and tested for 14 respiratory pathogens using multiplex reverse transcription-polymerase chain reaction.
  
  
  RESULTS
  Estimated incidence of ARI was 542 and 2691 per 1000 infant-years, and hospitalization rates for ARI were 81 and 138 per 1000 infant-years, in urban and semi-rural cohorts, respectively, from clinic- and hospital-based surveillance. However self-reported ARI episodes were just 1.5-fold higher in the semi-rural versus urban cohort, indicating that part of the urban-rural difference was explained by under-ascertainment in the urban cohort. Incidence was higher in infants ≥6 months of age than <6 months, but this was pathogen-specific. One or more viruses were detected in 53% (urban) and 64% (semi-rural) of samples from outpatients with ARI and in 78% and 66% of samples from hospitalized ARI patients, respectively. The most frequently detected viruses were rhinovirus, respiratory syncytial virus, influenza virus A and bocavirus. ARI-associated hospitalizations were associated with longer stays and more frequent ICU admission than other infections.
  
  
  CONCLUSIONS
  ARI is a significant cause of morbidity in Vietnamese infants and influenza virus A is an under-appreciated cause of vaccine-preventable disease and hospitalizations in this tropical setting. Public health strategies to reduce infant ARI incidence and hospitalization rates are needed.
authors: From the *Oxford University Clinical Research Unit, Wellcome Trust Major Overseas Programme, Ho Chi Minh City, Vietnam; †Centre for Tropical Medicine, Nuffield Department of Clinical Medicine, University of Oxford, United Kingdom; ‡Department of Epidemiology and Preventive Medicine, Monash University, Melbourne, Australia; §Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam; ¶Hung Vuong Hospital, Ho Chi Minh City, Vietnam; ‖Dong Thap Hospital, Cao Lanh, Vietnam; **District 8 Hospital, Ho Chi Minh City, Vietnam; ††Children's Hospital No. 1, Ho Chi Minh City, Vietnam; and ‡‡Department of Microbiology and Immunology, University of Melbourne, Australia.
authors: Katherine L
authors: KL
authors: Anders
authors: Hoa L
authors: HL
authors: Nguyen
authors: Nguyet Minh
authors: NM
authors: Nguyen
authors: Nguyen Thi
authors: NT
authors: Van Thuy
authors: Nguyen Thi
authors: NT
authors: Hong Van
authors: Nguyen Trong
authors: NT
authors: Hieu
authors: Nguyen Thi
authors: NT
authors: Hong Tham
authors: Phan Thi
authors: PT
authors: Thanh Ha
authors: Le Bich
authors: le B
authors: Lien
authors: Nguyen Van
authors: NV
authors: Vinh Chau
authors: Vu Thi
authors: VT
authors: Ty Hang
authors: H Rogier
authors: HR
authors: van Doorn
authors: Cameron P
authors: CP
authors: Simmons
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D006801:Humans; D015994:Incidence; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D060885:Multiplex Polymerase Chain Reaction; D009305:Nasopharynx / Q000821:virology; D011247:Pregnancy; D012136:Respiratory Syncytial Viruses; D012141:Respiratory Tract Infections / Q000453:epidemiology* / Q000821:virology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014744:Vietnam / Q000453:epidemiology; D014777:Virus Diseases / Q000453:epidemiology* / Q000821:virology*; D014780:Viruses / Q000302:isolation & purification*; D055815:Young Adult