title: Revisiting typhoid fever surveillance in low and middle income countries: lessons from systematic literature review of population-based longitudinal studies.
abstract: BACKGROUND
  The control of typhoid fever being an important public health concern in low and middle income countries, improving typhoid surveillance will help in planning and implementing typhoid control activities such as deployment of new generation Vi conjugate typhoid vaccines.
  
  
  METHODS
  We conducted a systematic literature review of longitudinal population-based blood culture-confirmed typhoid fever studies from low and middle income countries published from 1(st) January 1990 to 31(st) December 2013. We quantitatively summarized typhoid fever incidence rates and qualitatively reviewed study methodology that could have influenced rate estimates. We used meta-analysis approach based on random effects model in summarizing the hospitalization rates.
  
  
  RESULTS
  Twenty-two papers presented longitudinal population-based and blood culture-confirmed typhoid fever incidence estimates from 20 distinct sites in low and middle income countries. The reported incidence and hospitalizations rates were heterogeneous as well as the study methodology across the sites. We elucidated how the incidence rates were underestimated in published studies. We summarized six categories of under-estimation biases observed in these studies and presented potential solutions.
  
  
  CONCLUSIONS
  Published longitudinal typhoid fever studies in low and middle income countries are geographically clustered and the methodology employed has a potential for underestimation. Future studies should account for these limitations.
authors.affiliation: Policy and Economic Research Department, International Vaccine Institute, SNU Research Park, 1 Gwanak-ro, Gwanak-gu, Seoul, 151-742, South Korea. vmogasale@ivi.int.
authors.forename: Vittal
authors.initials: V
authors.lastname: Mogasale
authors.affiliation: Epidemiology Department, International Vaccine Institute, Seoul, South Korea. vijivittalmogasale@gmail.com.
authors.forename: Vijayalaxmi V
authors.initials: VV
authors.lastname: Mogasale
authors.affiliation: Policy and Economic Research Department, International Vaccine Institute, SNU Research Park, 1 Gwanak-ro, Gwanak-gu, Seoul, 151-742, South Korea. Enusa.Ramani@IVI.INT.
authors.forename: Enusa
authors.initials: E
authors.lastname: Ramani
authors.affiliation: Policy and Economic Research Department, International Vaccine Institute, SNU Research Park, 1 Gwanak-ro, Gwanak-gu, Seoul, 151-742, South Korea. jslee@ivi.int.
authors.forename: Jung Seok
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Biostatistics and Data Management Department, International Vaccine Institute, Seoul, South Korea. JuYeon.Park@IVI.INT.
authors.forename: Ju Yeon
authors.initials: JY
authors.lastname: Park
authors.affiliation: Biostatistics and Data Management Department, International Vaccine Institute, Seoul, South Korea. KangSungLee@IVI.INT.
authors.forename: Kang Sung
authors.initials: KS
authors.lastname: Lee
authors.affiliation: Development and Delivery Unit, International Vaccine Institute, Seoul, South Korea. twierzba@path.org.|PATH, 455 Massachusetts Avenue NW, Suite 1000, Washington, DC, USA. twierzba@path.org.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Wierzba
mesh_terms: D016208:Databases, Factual; D003906:Developing Countries; D006760:Hospitalization; D006801:Humans; D015994:Incidence; D008137:Longitudinal Studies; D012485:Salmonella typhi / Q000302:isolation & purification; D014435:Typhoid Fever / Q000453:epidemiology* / Q000382:microbiology
references.citation: Trop Med Int Health. 2011 Mar;16(3):314-23
references.pmid: 21223462
references.citation: BMJ. 2006 Jul 8;333(7558):78-82
references.pmid: 16825230
references.citation: Am J Trop Med Hyg. 2000 May;62(5):644-8
references.pmid: 11289678
references.citation: Vaccine. 1996 Apr;14(5):435-8
references.pmid: 8735556
references.citation: J Glob Health. 2012 Jun;2(1):010401
references.pmid: 23198130
references.citation: Lancet. 1991 Oct 26;338(8774):1055-9
references.pmid: 1681365
references.citation: Clin Infect Dis. 2012 Apr;54(8):1091-9
references.pmid: 22357703
references.citation: Emerg Infect Dis. 2010 Nov;16(11):1796-7
references.pmid: 21029549
references.citation: Lancet. 1999 Aug 28;354(9180):734-7
references.pmid: 10475185
references.citation: Int J Infect Dis. 2006 May;10(3):215-22
references.pmid: 16431148
references.citation: Pediatr Infect Dis J. 2010 Nov;29(11):1035-9
references.pmid: 21046701
references.citation: PLoS One. 2012;7(1):e29119
references.pmid: 22276105
references.citation: N Engl J Med. 2009 Jul 23;361(4):335-44
references.pmid: 19625715
references.citation: Int J Infect Dis. 2010 Sep;14 Suppl 3:e93-9
references.pmid: 20236850
references.citation: Wkly Epidemiol Rec. 2008 Feb 8;83(6):49-59
references.pmid: 18260212
references.citation: Am J Trop Med Hyg. 2006 Jan;74(1):114-9
references.pmid: 16407354
references.citation: J Infect Dev Ctries. 2013 Nov;7(11):781-7
references.pmid: 24240034
references.citation: Bull World Health Organ. 2008 Apr;86(4):260-8
references.pmid: 18438514
references.citation: Vaccine. 2012 Aug 3;30(36):5389-95
references.pmid: 22721899
references.citation: Bull World Health Organ. 2006 Jan;84(1):72-7
references.pmid: 16501718
references.citation: Lancet Glob Health. 2014 Oct;2(10):e570-80
references.pmid: 25304633
references.citation: PLoS One. 2012;7(12):e51823
references.pmid: 23284780
references.citation: Am J Trop Med Hyg. 2013 Jan;88(1):144-52
references.pmid: 23208887
references.citation: N Engl J Med. 2001 Apr 26;344(17):1263-9
references.pmid: 11320385
references.citation: Vaccine. 1990 Feb;8(1):81-4
references.pmid: 2180234
references.citation: Emerg Infect Dis. 2005 Feb;11(2):326-9
references.pmid: 15752457
references.citation: Lancet. 1990 Oct 13;336(8720):891-4
references.pmid: 1976928
references.citation: Emerg Infect Dis. 2003 May;9(5):539-44
references.pmid: 12737736
references.citation: Bull World Health Organ. 2001;79(7):625-31
references.pmid: 11477965
references.citation: Expert Rev Vaccines. 2013 Nov;12(11):1273-86
references.pmid: 24156285
references.citation: PLoS One. 2012;7(9):e44063
references.pmid: 22970162