Date: Mon 24 Dec 2012
From: Danuta Skowronski
[Re: ProMED-mail Novel coronavirus - Eastern Mediterranean (05): WHO, transmission route 20121223.1465597]
We would like to comment on 2 epidemiologic issues included in recent postings regarding the 2012 novel coronavirus (nCoV):
1. Failure (to date) of nCoV to transmit easily or sustainably between people.
This has been cited as an epidemiologic feature distinguishing nCoV from the 2003 SARS CoV. It is worth remembering, however, that despite being a substantial global concern, SARS CoV was also not generally very transmissible.  It required certain conditions of close contact (hospital or household) or facilitated transmission (aerosol generating procedures) to achieve person-to-person spread and was strikingly a nosocomial-associated infection throughout.
SARS CoV did not ultimately achieve the status of a pandemic, failing to exhibit widespread community transmission in most countries. Low inherent transmissibility combined with a delay in peak infectivity until well into the course of serious illness may explain why SARS was primarily a nosocomial infection; why so few countries experienced outbreaks; and why it could ultimately be extinguished. Seasonality may have also played a role. 
2. The "index case" for the April 2012 Jordan nCoV cluster could not be determined.
The index case in an epidemiologic investigation is the 1st recognized case. Lessons learned from SARS instead emphasize the importance of "Patient Zero", the 1st case whether initially recognized or not.  While this may seem a matter of semantics, the distinction has implications for the prevention of onward transmission.
Mathematical models for SARS, incorporating contact network theory, have stressed the importance of Patient Zero in predicting epidemic likelihood -- determined by the transmissibility of the agent, the number of contacts of Patient Zero, and the number of people infected between Patient Zero (the 1st case) and intervention on the index case (the 1st recognized case). 
Patient Zero thus tests the baseline capacity of a system to respond to emerging threats before they are known or recognized. 
As such, Patient Zero commands advance and ongoing attention to infection control precautions in the management of all SARI [severe acute respiratory illness], notably that of unknown etiology; emphasizes the need for strong, well-coordinated surveillance systems, with particular vigilance for clusters involving health care workers as signal if not incipient events; and underscores the need for efficient communication networks to disseminate public health alerts and enhance awareness before additional cases or clusters occur.