title: Influenza Pandemics and Tuberculosis Mortality in 1889 and 1918: Analysis of Historical Data from Switzerland.
abstract: BACKGROUND
  Tuberculosis (TB) mortality declined in the northern hemisphere over the last 200 years, but peaked during the Russian (1889) and the Spanish (1918) influenza pandemics. We studied the impact of these two pandemics on TB mortality.
  
  
  METHODS
  We retrieved historic data from mortality registers for the city of Bern and countrywide for Switzerland. We used Poisson regression models to quantify the excess pulmonary TB (PTB) mortality attributable to influenza.
  
  
  RESULTS
  Yearly PTB mortality rates increased during both influenza pandemics. Monthly influenza and PTB mortality rates peaked during winter and early spring. In Bern, for an increase of 100 influenza deaths (per 100,000 population) monthly PTB mortality rates increased by a factor of 1.5 (95%Cl 1.4-1.6, p<0.001) during the Russian, and 3.6 (95%Cl 0.7-18.0, p = 0.13) during the Spanish pandemic. Nationally, the factor was 2.0 (95%Cl 1.8-2.2, p<0.001) and 1.5 (95%Cl 1.1-1.9, p = 0.004), respectively. We did not observe any excess cancer or extrapulmonary TB mortality (as a negative control) during the influenza pandemics.
  
  
  CONCLUSIONS
  We demonstrate excess PTB mortality during historic influenza pandemics in Switzerland, which supports a role for influenza vaccination in PTB patients in high TB incidence countries.
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Zürcher
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
authors.forename: Marcel
authors.initials: M
authors.lastname: Zwahlen
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
authors.forename: Marie
authors.initials: M
authors.lastname: Ballif
authors.affiliation: Epidemiology, Biostatistics and Prevention Institute, University of Zürich, Zürich, Switzerland.
authors.forename: Hans L
authors.initials: HL
authors.lastname: Rieder
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.
authors.forename: Matthias
authors.initials: M
authors.lastname: Egger
authors.affiliation: Institute of Social and Preventive Medicine, University of Bern, Bern, Switzerland.|Swiss Tropical and Public Health Institute, Basel, Switzerland.|University of Basel, Basel, Switzerland.
authors.forename: Lukas
authors.identifier: http://orcid.org/0000-0003-3309-4835
authors.initials: L
authors.lastname: Fenner
mesh_terms: D016208:Databases, Factual; D049672:History, 19th Century; D049673:History, 20th Century; D006801:Humans; D007251:Influenza, Human / Q000150:complications / Q000453:epidemiology*; D058873:Pandemics / Q000266:history; D016012:Poisson Distribution; D012426:Russia / Q000453:epidemiology; D012621:Seasons; D013030:Spain / Q000453:epidemiology; D016019:Survival Analysis; D013557:Switzerland; D014376:Tuberculosis / Q000209:etiology / Q000401:mortality*