Consider doing an epidemic study and have collected data on the index/primary case. Three months thereafter you are told of someone who died four months prior to the start of your study and with all the signs and symptoms of the disease you are investigating. Will you consider the disease and this new information as your primary case or should you simply ignore the disease?
It depends on your case definition, which depends on time, place and person. By extending the timeframe backwards, you capture your other case who is now the index case. This also depends on the incubation period of the infection you are considering.
Agree. It also depends what is the purpose of your investigation. Is this for quantifying and understanding the problem, or containment? For the former it is another case you may consider as a potential early case, for the latter you would need to follow a new set of contacts.
Luis i appreciate your insight. It is for both ie understanding the outbreak origin and containment purpose. Considering 'patient zero' will enable us to estimate the start of the epidemic although this can be estimated using epicurve but it can also help us to evaluate ongoing containment effort.
It is Wikipedia, but for a basic learning I think it is great!
http://en.wikipedia.org/wiki/Index_case
First it is important in order to confirm the case on the basis of definition, this information may be by the lay man or suspected and not probable or confirmed diagnosis was not made. Second we can know the incubation period from the epidemic curve, as the death occurs four months prior to the so called second epidemic or outbreak. There may be infection due to the same source. But HIV cases with prolong the incubation period may have patient zero.In this case, we should also count such case as of Patient Zero.
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