Limits...
Theoretical perspectives on the infectiousness of Ebola virus disease.

Nishiura H, Chowell G - Theor Biol Med Model (2015)

Bottom Line: Whereas R0 of EVD is similar to that of influenza, the growth rate (i.e. the measure of infectiousness per unit time) for EVD was shown to be comparatively lower than that for influenza.Moreover, EVD and influenza differ in mode of transmission whereby the probability of transmission per contact is lower for EVD compared to that of influenza.Descriptions and interpretations of different variables quantifying infectiousness need to be used clearly and objectively in the scientific community and for risk communication.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. nishiurah@m.u-tokyo.ac.jp.

ABSTRACT

Background: Ebola virus disease (EVD) has generated a large epidemic in West Africa since December 2013. This mini-review is aimed to clarify and illustrate different theoretical concepts of infectiousness in order to compare the infectiousness across different communicable diseases including EVD.

Methods: We employed a transmission model that rests on the renewal process in order to clarify theoretical concepts on infectiousness, namely the basic reproduction number, R0, which measures the infectiousness per generation of cases, the force of infection (i.e. the hazard rate of infection), the intrinsic growth rate (i.e. infectiousness per unit time) and the per-contact probability of infection (i.e. infectiousness per effective contact).

Results: Whereas R0 of EVD is similar to that of influenza, the growth rate (i.e. the measure of infectiousness per unit time) for EVD was shown to be comparatively lower than that for influenza. Moreover, EVD and influenza differ in mode of transmission whereby the probability of transmission per contact is lower for EVD compared to that of influenza.

Conclusions: The slow spread of EVD associated with the need for physical contact with body fluids supports social distancing measures including contact tracing and case isolation. Descriptions and interpretations of different variables quantifying infectiousness need to be used clearly and objectively in the scientific community and for risk communication.

Show MeSH

Related in: MedlinePlus

Comparison of the intrinsic growth rate of infectious diseases. (A) For a given R0 and the mean generation time Tg for a given infectious disease, the curves show the relationship between the intrinsic growth rate (r) and the coefficient of variation of the generation time of the disease. r of measles is the largest, followed by influenza, and then Ebola virus disease (EVD). (B) Temporal evolution in the number of new cases of measles, influenza, and Ebola virus disease using a coefficient of variation of the generation time at 50%. Parameter values are given in Table 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
getmorefigures.php?uid=PMC4430046&req=5

Fig1: Comparison of the intrinsic growth rate of infectious diseases. (A) For a given R0 and the mean generation time Tg for a given infectious disease, the curves show the relationship between the intrinsic growth rate (r) and the coefficient of variation of the generation time of the disease. r of measles is the largest, followed by influenza, and then Ebola virus disease (EVD). (B) Temporal evolution in the number of new cases of measles, influenza, and Ebola virus disease using a coefficient of variation of the generation time at 50%. Parameter values are given in Table 1.

Mentions: It should be noted that it is possible that the right-tail of g(s) for EVD might have been underestimated if there were substantial number of secondary transmissions from deceased persons during funerals. Adopting the values of R0 and Tg given in Table 1, and assuming that the coefficient of variation of the generation time at 50%, the intrinsic growth rate of influenza H1N1-2009 is calculated as 0.125 per day, while that of EVD is calculated as 0.038 per day. Figure 1A compares the growth rates (r) of three representative communicable diseases for different values of the coefficient of variation of the generation time. An epidemic of measles appears to grow the fastest followed by one of influenza while an outbreak of EVD is expected to grow the slowest. Whereas the R0 for EVD is similar to that of influenza, the growth rate of EVD is far smaller than that of influenza. This is because each disease generation in the context of EVD transmission takes approximately two weeks, while each generation of new influenza cases occurs on a much shorter time scale - every 3 days on average. Moreover, EVD spreads comparatively slowly mainly by physical contact. This feature indicates that social distancing measures including contact tracing and case isolation could be powerful options for controlling EVD assuming that public health infrastructure exists for these interventions to be feasible [27].Figure 1


Theoretical perspectives on the infectiousness of Ebola virus disease.

Nishiura H, Chowell G - Theor Biol Med Model (2015)

Comparison of the intrinsic growth rate of infectious diseases. (A) For a given R0 and the mean generation time Tg for a given infectious disease, the curves show the relationship between the intrinsic growth rate (r) and the coefficient of variation of the generation time of the disease. r of measles is the largest, followed by influenza, and then Ebola virus disease (EVD). (B) Temporal evolution in the number of new cases of measles, influenza, and Ebola virus disease using a coefficient of variation of the generation time at 50%. Parameter values are given in Table 1.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4430046&req=5

Fig1: Comparison of the intrinsic growth rate of infectious diseases. (A) For a given R0 and the mean generation time Tg for a given infectious disease, the curves show the relationship between the intrinsic growth rate (r) and the coefficient of variation of the generation time of the disease. r of measles is the largest, followed by influenza, and then Ebola virus disease (EVD). (B) Temporal evolution in the number of new cases of measles, influenza, and Ebola virus disease using a coefficient of variation of the generation time at 50%. Parameter values are given in Table 1.
Mentions: It should be noted that it is possible that the right-tail of g(s) for EVD might have been underestimated if there were substantial number of secondary transmissions from deceased persons during funerals. Adopting the values of R0 and Tg given in Table 1, and assuming that the coefficient of variation of the generation time at 50%, the intrinsic growth rate of influenza H1N1-2009 is calculated as 0.125 per day, while that of EVD is calculated as 0.038 per day. Figure 1A compares the growth rates (r) of three representative communicable diseases for different values of the coefficient of variation of the generation time. An epidemic of measles appears to grow the fastest followed by one of influenza while an outbreak of EVD is expected to grow the slowest. Whereas the R0 for EVD is similar to that of influenza, the growth rate of EVD is far smaller than that of influenza. This is because each disease generation in the context of EVD transmission takes approximately two weeks, while each generation of new influenza cases occurs on a much shorter time scale - every 3 days on average. Moreover, EVD spreads comparatively slowly mainly by physical contact. This feature indicates that social distancing measures including contact tracing and case isolation could be powerful options for controlling EVD assuming that public health infrastructure exists for these interventions to be feasible [27].Figure 1

Bottom Line: Whereas R0 of EVD is similar to that of influenza, the growth rate (i.e. the measure of infectiousness per unit time) for EVD was shown to be comparatively lower than that for influenza.Moreover, EVD and influenza differ in mode of transmission whereby the probability of transmission per contact is lower for EVD compared to that of influenza.Descriptions and interpretations of different variables quantifying infectiousness need to be used clearly and objectively in the scientific community and for risk communication.

View Article: PubMed Central - PubMed

Affiliation: Graduate School of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. nishiurah@m.u-tokyo.ac.jp.

ABSTRACT

Background: Ebola virus disease (EVD) has generated a large epidemic in West Africa since December 2013. This mini-review is aimed to clarify and illustrate different theoretical concepts of infectiousness in order to compare the infectiousness across different communicable diseases including EVD.

Methods: We employed a transmission model that rests on the renewal process in order to clarify theoretical concepts on infectiousness, namely the basic reproduction number, R0, which measures the infectiousness per generation of cases, the force of infection (i.e. the hazard rate of infection), the intrinsic growth rate (i.e. infectiousness per unit time) and the per-contact probability of infection (i.e. infectiousness per effective contact).

Results: Whereas R0 of EVD is similar to that of influenza, the growth rate (i.e. the measure of infectiousness per unit time) for EVD was shown to be comparatively lower than that for influenza. Moreover, EVD and influenza differ in mode of transmission whereby the probability of transmission per contact is lower for EVD compared to that of influenza.

Conclusions: The slow spread of EVD associated with the need for physical contact with body fluids supports social distancing measures including contact tracing and case isolation. Descriptions and interpretations of different variables quantifying infectiousness need to be used clearly and objectively in the scientific community and for risk communication.

Show MeSH
Related in: MedlinePlus