Choose the option that best answers the question.

Malaria is an infectious disease that kills more than 600,000 people every year. Several species of the genus Plasmodium cause malaria, with two of the most common being Plasmodium falciparum and Plasmodium vivax. Though both species cause a very similar illness, P. falciparum malaria is more likely to result in fatalities than P. vivax malaria, while P. vivax malaria is more likely to recur -- to return after a period of time during which the patient is healthy and has no parasites present in the blood.

The two species of malaria parasites respond differently to antimalarial medications, but in many areas where malaria is common, testing to determine what type of malaria a patient has is not widely available. Therefore malaria treatments are often tested against both species of the parasite, and first-line malaria treatments in these regions ideally should be effective against both parasites.

Experiment 1

For many years, public health professionals in Papua New Guinea have recommended a treatment regimen, Drug Combination A, as a first-line malaria treatment. Recently a new treatment regimen, Drug Combination B, has been proposed as a potential replacement for Combination A, and a study was conducted to compare their effectiveness.

Children entering a local health clinic with malaria symptoms were tested to determine which Plasmodium species they carried. The patients were then randomly assigned Drug Combination A or Drug Combination B, and their blood was tested periodically for the presence of parasites. 

Figure 1

Experiment 2

On rare occasions, patients have severe allergic reactions to a compound that is found in both Drug Combination A and Drug Combination B. In these cases, a second-line treatment must be used. A second study was conducted to determine which of several drug combinations would be the best second-line drug to recommend for use in Papua New Guinea. Table 1 shows the treatment response to the second-line drug combinations.

Table 1

If 1000 patients in the P. falciparum group were treated with Drug Combination B in Experiment 1, approximately how many of those patients remained infected on Day 7?