Essay: Understanding the Spread of SARS and Implications for Disease Outbreak Response

1. I feel that the two overall goals of Lipsitch et al were to describe how the SARS outbreak might have progressed and inform people how to properly respond to a disease outbreak. Since the authors consider four different possibilities when estimating their R value, they are looking at how the disease might have progressed through Hong Kong; these different possibilities involves a different number of index cases and a different period of time for the initial outbreak. Additionally, their R estimate factors in the control measures that were applied after the outbreak. If the pattern of spread through Hong Kong can be understood, then it would be possible to identify outbreaks in other cities before they reached the point of rapid growth. As the authors provided information on the best ways to limit a disease outbreak, I feel that their model can be applied to other viruses, especially respiratory viruses. As SARS is a member of the coronavirus family, this model and the findings of the paper could be applied to other outbreaks to reduce the spread time and number of people infected.
2. Figure 1B is showing the numbers of secondary cases infected by one index case throughout the weeks of a beginning epidemic. These graph trends also reflect the characteristics of a superspreader, as that involves one index case infecting several other cases. The y-axis records the number of secondary cases infected, in factors of 5. The x-axis shows the weeks of the outbreak. The circles on the individual lines show the average number of cases, while the error bars show the maximum and minimum number of secondary cases. The horizontal line at y = 1 is representing the minimum R growth value needed for the spread of an epidemic. If the average number of secondary cases was below 1, then that would suggest that the epidemic is slowing down in expansion. If the average number of secondary cases was above 1, then this would suggest rapid growth of the epidemic. As shown in Figure 1B, the growth of the SARS epidemic was slowing down towards the weeks of April, as the last three values for average number of secondary cases were below 1. However, two of the weeks in March also had a value below 1, but this jumped back up again in the following weeks. Therefore, the SARS epidemic might be working in a cyclical pattern as the rate of growth decreases then increases.
3. A “superspreader” is an infected individual that passes the virus along to many other individuals. Theoretically, the original individual would be in close contact with many people throughout the day to spread their infection so widely. It is important for the authors to account for superspreaders as they could change the timing of the outbreak, as well as give more insight to mode of transmission. Additionally, if a person is able to infect many other people, then this would suggest that the mortality rate for this disease is not alarmingly high as the virus was able to infect one person and be spread among others. Furthermore, the presence of superspreaders could change the rate of the infection growth since these individuals are linked to high probabilities of infections but this may not hold true for the normal population. Recognizing superspreaders could help the authors narrow down the timing of the beginning of their outbreak and determine what the possible range of the outbreak is. Additionally, the superspreaders could provide insight as to how the disease originally entered the human population.
4. As one of the major parts of the Lipsitch et al papers was the consideration for asymptomatic cases, this could be very relevant in controlling a MERS outbreak; this is due to the fact that the initial symptoms in a MERS case can be widely varied, such that a mild case might not be suspected as MERS and so they further contribute to the spread of the illness. Additionally, the conclusion that the implementation of early control measures, such as isolation and quarantine, is highly effective at preventing an epidemic is relevant to MERS. Since the cause and most of the background of MERS was unknown at the time of the article, it might be more practical for healthcare providers to implement isolation and quarantine rather than trying to treat cases. Furthermore, as there is a question as to the spillover between humans and animal carriers, isolation and quarantine would prevent some further contact between animals and humans. Oppositely, the assumption by the authors that the number of contacts from each index case was independent of population density is not relevant to the MERS outbreak. It has been observed that MERS has a high propensity to spread among hospital patients and other immunocompromised individuals. Cities with higher population densities are more likely to have larger hospitals and therefore more interactions between infected individuals and susceptible individuals. Additionally, large cities may have more overcrowded hospitals and even further increase the rate of infection for a MERS outbreak. If the relationship between population density and number of contacts is still considered to be non-existent in the MERS outbreak, this could cause more individuals to become infected as some contacts are overlooked for quarantine or other disease management.