title: Reported co-infection deaths are more common in early adulthood and among similar infections.
abstract: BACKGROUND
  Many people have multiple infections at the same time, but the combined contribution of those infections to disease-related mortality is unknown. Registered causes of death offer a unique opportunity to study associations between multiple infections.
  
  
  METHODS
  We analysed over 900,000 death certificates that reported infectious causes of death. We tested whether reports of multiple infections (i.e., co-infections) differed across individuals' age or sex. We also tested whether each pair of infections were reported together more or less often than expected by chance, and whether this co-reporting was associated with the number of biological characteristics they had in common.
  
  
  RESULTS
  In England and Wales, and the USA, 10 and 6 % respectively of infection-related deaths involved co-infection. Co-infection was reported reported most often in young adults; 30 % of infection-related deaths among those aged 25-44 from the USA, and 20 % of infection-related deaths among those aged 30-39 from England and Wales, reported multiple infections. The proportion of infection-related deaths involving co-infection declined with age more slowly in males than females, to less than 10 % among those aged >65. Most associated pairs of infections co-occurred more often than expected from their frequency of being reported alone (488/683 [71 %] in the USA, 129/233 [55 %] in England and Wales), and tended to share biological characteristics (taxonomy, transmission mode, tropism or timescale).
  
  
  CONCLUSIONS
  Age, sex, and biologically similar infections are associated with death from co-infection, and may help indicate patients at risk of severe co-infection.
authors.affiliation: Department of Animal and Plant Sciences, University of Sheffield, Alfred Denny Building, Western Bank, Sheffield, S10 2TN, UK. emilycgri@gmail.com.|Department of Entomology, North Carolina State University, Campus Box 7613, Gardner Hall, Raleigh, NC, 27695-7613, USA. emilycgri@gmail.com.
authors.forename: E C
authors.initials: EC
authors.lastname: Griffiths
authors.affiliation: Centre for Immunology, Infection and Evolution & Institute of Evolutionary Biology, School of Biological Sciences, Ashworth Labs, University of Edinburgh, Kings Buildings, Charlotte Auerbach Road, Edinburgh, EH9 3FL, UK. amy.pedersen@ed.ac.uk.
authors.forename: A B
authors.initials: AB
authors.lastname: Pedersen
authors.affiliation: Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK. A.Fenton@liverpool.ac.uk.
authors.forename: A
authors.initials: A
authors.lastname: Fenton
authors.affiliation: Institute of Evolutionary Biology and Environmental Studies, University of Zürich, Winterthurerstrasse, Zürich, 8057, Switzerland. owen.petchey@ieu.uzh.ch.
authors.forename: O L
authors.initials: OL
authors.lastname: Petchey
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002423:Cause of Death; D002648:Child; D002675:Child, Preschool; D060085:Coinfection / Q000401:mortality*; D004739:England / Q000453:epidemiology; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008875:Middle Aged; D014481:United States / Q000453:epidemiology; D014852:Wales / Q000453:epidemiology; D055815:Young Adult