In July 2014, when Africa was experiencing a devastating outbreak of the deadly Ebola virus, doctors identified the first Ebola case in Nigeria. Officials worried that Ebola would quickly spread in Nigeria, but within three months, health officials had defeated the disease inside Nigeria's borders. Because Ebola spreads through direct contact with an infected person, Nigerian medical personnel immediately tracked down everyone who had been in contact with the infected patient. More than one hundred and fifty workers conducted 18,500 interviews to identify everyone who might have been exposed to Ebola. The medical personnel monitored these contacts, isolating and treating anyone who showed signs of the disease. These tactics succeeded, and Nigeria was declared free of Ebola in October. Which organizational structure does this text primarily use?

proplem-solution or compare -contrast?