One of the first critical steps in understanding any outbreak of a novel infectious disease is to conduct a `case-control’ study, where a number of known infected individuals are compared to a much larger number of controls, matched for age, sex, and neighborhood.
A couple of weeks ago, in CDC: Risk Factors Involved With H7N9 Infection, we looked at a case control study that was begun in China literally just weeks after the first cases of H7N9 infection were identified in the spring of 2013.
For well over a year the World Health Organization, and many other scientists, have been urging the Saudi’s to conduct this sort of epidemiological investigation, with the WHO publishing framework for just such a project a year ago (see case-control study protocol Jul 2013).
Today, more than two years into the emergence of the MERS virus, Reuters is reporting that Saudi Arabia has begun the process of conducting a case-control study.
Saudi Arabia says it has recruited patients for a crucial study on the source of the deadly MERS virus, acknowledging it is late but pledging more work on the epidemic after international criticism of its slow response.
Scientists and global public health experts have faulted Saudi Arabia's response for allowing the spread of the Middle East Respiratory Syndrome (MERS) virus, which has now killed nearly 300 people inside the kingdom.
Among Riyadh's failings has been the lack of a type of research known as a "case-control" study, which compares the histories of people with a disease to a "control group" of people who do not have it, to try to determine what causes it.
The kingdom's chief scientist, Tariq Madani, said the study was now under way, having so far enrolled the first 10 "cases" - people who had the disease and either died or recovered - alongside 40 "controls" to compare them with. Ideally, the study would look at 20 cases and 80 controls, he said.
The sample size mentioned - 20 cases & 80 controls - is considerably smaller than the Chinese H7N9 case-control study mentioned above which used 89 laboratory-confirmed A(H7N9) cases matched to 339 controls.
I’ll leave it to those better versed in these sorts of studies to weigh in on the `ideal’ size of such a study.