Household transmission and disease transmissibility of a large HAV outbreak in Lazio, Italy, 2016–2017

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A major outbreak of Hepatitis A Virus (HAV) has swept through Europe between mid-2016 and 2017, mainly within the community of men who have sex with men (MSM). Over the same period, about 1000 outbreak-related cases of acute Hepatitis A (AHA) were recorded in Lazio region, Italy. We calibrated a Bayesian model to reconstruct likely transmission events within all 44 households where multiple infections were recorded, representing a total of 103 cases from the HAV outbreak in Lazio. Based on information on the observed times of symptom onset, we estimated the probability distribution function of the HAV generation time and used it to compute the effective and instantaneous reproduction numbers for the considered outbreak from the overall epidemic curve (N = 998 cases). We estimated a mean generation time of 30.2 days (95%CI: 25.2–33.0) and an effective reproduction number of about 1.63 (95% CI: 1.35–1.94). Transmissibility peaked in January 2017, shortly before targeted awareness and vaccination campaigns were put in place by health authorities; however, transmission remained above the epidemic threshold until June 2017. Within households, children (0–15) and young adults (16–30) infected preferentially individuals of the same age class, whereas transmission within older age groups was substantially homogeneous. These results suggest that the implemented interventions were able to slow down HAV transmission, but not to bring it rapidly to a halt. According to our estimates of the HAV transmissibility, about 50% of the at-risk persons should be immunized to prevent similar outbreaks in the future. Our results also indicate spillover from community transmission to household members, suggesting the opportunity of vaccinating household contacts of cases to prevent further spread of the epidemics.

Original languageEnglish
Article number100351
Pages (from-to)1-5
Number of pages5
Publication statusE-pub ahead of print - Jun 13 2019


  • Acute hepatitis A
  • Bayesian model
  • HAV
  • Household transmission
  • Outbreak

ASJC Scopus subject areas

  • Epidemiology
  • Parasitology
  • Microbiology
  • Public Health, Environmental and Occupational Health
  • Infectious Diseases
  • Virology


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