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How would the Ro differ if you analysed the import of Ebola to Dallas?
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The Ro figure quoted is - as acknowledged - very much higher than recent estimates of 1.5-2.0. An interesting comparison could be made with the arrival in Dallas of an asymptomatic individual who became symptomatic, presented at hospital, returned to the community and was only admitted three days later. Considering the time that has subsequently elapsed it appears clear that there were only two nosocomial transmissions in this instance. There may be differences in clinical presentation which account for the markedly different outcomes of these two introductions. Nevertheless, I think this deserves comment. It is estimated that there will be ~3 asymptomatic exports from West Africa a month and the range of potential secondary cases is therefore of significant concern to the countries that will import them.

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The R0 of the index case in Dallas would simply be 2 and there were no tertiary cases. To my knowledge, both index cases in Dallas and Lagos were highly symptomatic. Control measures were rapidly implemented once the index patient in Dallas was admitted to the hospital for the second time. In Lagos, there was a delay of a few days which might explain the higher number of secondary cases. Also, the behavior of the index patient in Lagos while in hospital isolation could have facilitated transmission. Together, the two cases suggest that most transmissions happen during the late stages of the disease, as no (Dallas) or only a few (Lagos) infections of non-health care workers occurred.

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With thanks. I appreciate the Ro would be 2 in Dallas. I think your final sentence is important. It suggests the entry screening and Maine quarantine are superfluous, but emphasises the need for vigilance and prompt response should symptoms develop.

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