Countries like Brazil (which the article focuses on) are being left behind in the race to treat & contain the coronavirus pandemic the world is facing. Most testing is being focused on American & European cities right now, and consequently this is also where many of the critical chemicals and testing kits are being sent to. Because of this, officials really don't have a good idea of how badly the virus is spreading through Brazil. To directly quote the article, "Testing is the first defense against the virus and an important tool to stop so many patients from ending up hospitalized." Brazil is heavily reliant on international manufacturers for the chemicals and equipment needed to process the tests, so unfortunately there really isn't anything they can do about this unprecedented worldwide shortage.
To make matters worse, cities like Rio are famous for their favelas, in which large groups of people are living right on top of each other (literally) which provides the perfect breeding grounds for rapid spreading of the disease. Coupling this with the not-so-great track record of healthcare in this region, and there is some serious potential for a lot of people to suffer and die from COVID-19 in Brazil, and other developing countries around the world.