According to Federal health officials ,the fact that more West Nile cases have been reported indicates that

C
52.C 【精析】该题为细节题。第二段第四句“Federal. health officials are still trying to figure out why, but say they may be finding more West Nile precisely because they're on the lookout for it.”中的“be on the lookout for something”意为“注意，留心，警戒”，由此我们知道，联邦公共卫生官员仍然在寻找病毒蔓延的原因，但是认为因为他们对病毒的警惕性高，因此才可能会发现更多的感染者。故只有C项的表述正确。