Temporally Varying Relative Risks for Infectious Diseases

Abstract

Risks for disease in some population groups relative to others (relative risks) are usually considered to be consistent over time, though they are often modified by other, non-temporal factors. For infectious diseases, in which overall incidence often varies substantially over time, the patterns of temporal changes in relative risks can inform our understanding of basic epidemiologic questions. For example, recent work suggests that temporal changes in relative risks of infection over the course of an epidemic cycle can both be used to identify population groups that drive infectious disease outbreaks, and help elucidate differences in the effect of vaccination against infection (that is relevant to transmission control) compared with its effect against disease episodes (that reflects individual protection). Patterns of change in the in age groups affected over the course of seasonal outbreaks can provide clues to the types of pathogens that could be responsible for diseases for which an infectious cause is suspected. Changing apparent efficacy of vaccines during trials may provide clues to the vaccine's mode of action and/or indicate risk heterogeneity in the trial population. Declining importance of unusual behavioral risk factors may be a signal of increased local transmission of an infection. We review these developments and the related public health implications.

On the role of different age groups during pertussis epidemics in California, 2010 and 2014

“…[18] vs [19]) suggests the temporal changes in the role of different age groups during pertussis epidemics. In this paper, we use the previously developed methodology based on the relative risk (RR) statistic [20][21][22] to examine the roles of different age groups during the 2010 and the 2014 pertussis outbreaks in California, and compare those roles for the two epidemics. Our results suggest the prominence of adolescents aged 14-15 year during the 2014 pertussis epidemic, followed by adolescents aged 16-19 years and 11-13 years.…”

“…In this paper, we apply the methodology in [20][21][22] to assess the relative roles of different age groups during the 2010 and 2014 pertussis outbreaks in California. Quantification of the relative role for an age group according to the methodology in [20][21][22] is related to the impact of vaccination of an individual in that age group at the start of an epidemic on reducing the epidemic's initial growth rate/reproductive number (Supporting Information in each of [16,20,22]). Additionally, we examine the differences in the role of different age groups during the 2014 vs. the 2010 epidemic.…”

On the relative role of different age groups during epidemics associated with the respiratory syncytial virus

“…The latter might introduce a bias in the RR estimates for a number of RSV seasons, and the scope of that bias is difficult to assess with the available data. We also note that annual rates of RSV hospitalization in different age groups (Table 1) suggest temporal (year-toyear) changes in testing practices; however this should not bias the RR estimates that are derived separately during each season, unless testing/diagnostic practices change through the course of the season in a manner that is not uniform for all age groups [15,17].…”

Real-time analysis of the diphtheria outbreak in forcibly displaced Myanmar nationals in Bangladesh

“…Whereas we assumed that the susceptibility was greatest in the age group of 5-14 years, the proportion of cases in the age group of 15 years and above was higher before the epidemic peak than after. This may indicate either that adults made a substantial contribution to transmission during the epidemic growth phase [21] , or that relative age-specific reporting changed during the course of the outbreak.…”