Incubation Periods of Viral Gastroenteritis
Estimations of the incubation period of infectious diseases including gastroenteritis are critical to assure rationale, evidence based interventions to abort ongoing transmission. In our review of three major viral causes of gastroenteritis, we found that 61% of the 226 incubation period estimates given with a citation. After examining the citation trees for these estimates, only 114 (50%) of the 226 were actually based on data. Twenty-three (17%) sourced estimates cited an article that contained an unsourced estimate. These findings indicate that the incubation periods of enteric viruses are often considered common knowledge. Of the sources that were based on data, the majority for each virus could be traced back to an estimate from one of a small number of original studies, such as the Kaplan et al. articles for norovirus genogroups I and II.
There was some concern that individual studies could potentially be overly influential in pooled analysis. We conducted a sensitivity analysis by removing each study and recalculating the incubation period estimates. We found no qualitative difference in the results.
Determining the incubation period is limited by the level of uncertainty as to the time of infection. Because the incubation periods for viral gastroenteritis are short, it is often difficult to differentiate between primary and secondary cases in an outbreak. This makes obtaining accurate exposure interval information difficult. Most observational studies, particularly foodborne outbreak investigations, address this issue by only considering cases within some number of days after exposure. This method of case identification may introduce bias by eliminating cases that fall in the tail end of the incubation period distribution. While there are a wealth of observational studies that describe outbreaks caused by rotavirus and astrovirus, because the exposure interval for individual cases cannot be determined, the data from these studies cannot be used to determine the incubation period.
Numerous factors could cause data from experimental infection to differ from that of natural infection, such as the infectious dose or volunteers whose host status differs from that of the general population. For example, the sole experimental study contributing data to the pooled analysis for rotavirus sought volunteers with low serum antibody levels. These biases are compounded by the impossibility of performing experimental challenge studies in the populations most at risk for disease, children and the elderly. This is especially true for rotavirus and astrovirus, diseases that almost exclusively affect young children.
This review was limited by our inclusion only of published data and by our search terms. Due to our inclusion of some form of "incubation period" in searching for articles, the entirety of the literature on each virus was not reviewed. Our estimates for astrovirus and rotavirus are each based on three studies and fewer than 20 observations. Due to difficulties in studying these diseases experimentally, careful observational studies are needed to provide more evidence to support the incubation period and its distribution.
Accurate knowledge of incubation period is particularly important for viral gastroenteritis because of the short incubation period duration, relatively high secondary attack rate, and potential for healthcare associated outbreaks. Both rotavirus and norovirus are particularly difficult to control in the healthcare setting. Fischer and colleagues determined that a median of 27% of patients in developed countries and 32% of patients in developing countries discharged with a diagnosis of rotavirus had acquired the virus in the hospital. Furthermore, the incubation period is an important component of the serial interval (difference in symptom onset times in a case and those that case infects), which is one of the fundamental determinants of how quickly epidemics spread in a population.
Despite the licensure of two safe and efficacious vaccines, rotavirus continues to be an important public health problem. This is especially true in developing countries where the vast majority of rotavirus disease and deaths occur, and where rotavirus vaccine has been found to have the lowest efficacy. Accurate knowledge of the incubation period is important to understand dynamics of rotavirus disease and control. As vaccine coverage improves and rotavirus infection becomes no longer universal, the incubation period will be useful to study pathogen exposure related to vaccine failure and potential differences in host susceptibility to infection.
Discussion
Estimations of the incubation period of infectious diseases including gastroenteritis are critical to assure rationale, evidence based interventions to abort ongoing transmission. In our review of three major viral causes of gastroenteritis, we found that 61% of the 226 incubation period estimates given with a citation. After examining the citation trees for these estimates, only 114 (50%) of the 226 were actually based on data. Twenty-three (17%) sourced estimates cited an article that contained an unsourced estimate. These findings indicate that the incubation periods of enteric viruses are often considered common knowledge. Of the sources that were based on data, the majority for each virus could be traced back to an estimate from one of a small number of original studies, such as the Kaplan et al. articles for norovirus genogroups I and II.
There was some concern that individual studies could potentially be overly influential in pooled analysis. We conducted a sensitivity analysis by removing each study and recalculating the incubation period estimates. We found no qualitative difference in the results.
Determining the incubation period is limited by the level of uncertainty as to the time of infection. Because the incubation periods for viral gastroenteritis are short, it is often difficult to differentiate between primary and secondary cases in an outbreak. This makes obtaining accurate exposure interval information difficult. Most observational studies, particularly foodborne outbreak investigations, address this issue by only considering cases within some number of days after exposure. This method of case identification may introduce bias by eliminating cases that fall in the tail end of the incubation period distribution. While there are a wealth of observational studies that describe outbreaks caused by rotavirus and astrovirus, because the exposure interval for individual cases cannot be determined, the data from these studies cannot be used to determine the incubation period.
Numerous factors could cause data from experimental infection to differ from that of natural infection, such as the infectious dose or volunteers whose host status differs from that of the general population. For example, the sole experimental study contributing data to the pooled analysis for rotavirus sought volunteers with low serum antibody levels. These biases are compounded by the impossibility of performing experimental challenge studies in the populations most at risk for disease, children and the elderly. This is especially true for rotavirus and astrovirus, diseases that almost exclusively affect young children.
This review was limited by our inclusion only of published data and by our search terms. Due to our inclusion of some form of "incubation period" in searching for articles, the entirety of the literature on each virus was not reviewed. Our estimates for astrovirus and rotavirus are each based on three studies and fewer than 20 observations. Due to difficulties in studying these diseases experimentally, careful observational studies are needed to provide more evidence to support the incubation period and its distribution.
Accurate knowledge of incubation period is particularly important for viral gastroenteritis because of the short incubation period duration, relatively high secondary attack rate, and potential for healthcare associated outbreaks. Both rotavirus and norovirus are particularly difficult to control in the healthcare setting. Fischer and colleagues determined that a median of 27% of patients in developed countries and 32% of patients in developing countries discharged with a diagnosis of rotavirus had acquired the virus in the hospital. Furthermore, the incubation period is an important component of the serial interval (difference in symptom onset times in a case and those that case infects), which is one of the fundamental determinants of how quickly epidemics spread in a population.
Despite the licensure of two safe and efficacious vaccines, rotavirus continues to be an important public health problem. This is especially true in developing countries where the vast majority of rotavirus disease and deaths occur, and where rotavirus vaccine has been found to have the lowest efficacy. Accurate knowledge of the incubation period is important to understand dynamics of rotavirus disease and control. As vaccine coverage improves and rotavirus infection becomes no longer universal, the incubation period will be useful to study pathogen exposure related to vaccine failure and potential differences in host susceptibility to infection.
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