KINSHASA, Congo — Congo’s fight to rein in a deadly Ebola outbreak has authorities crossing the border to buy up available thermometers, a World Health Organization official said as the health ministry Thursday announced that confirmed cases had reached 31, including nine deaths. The spread of the often lethal hemorrhagic fever to a provincial capital of 1.2 million people has health officials scrambling to monitor for Ebola at busy ports in the capital, Kinshasa, which is downstream from the infected city of Mbandaka on the Congo River. Mbandaka is one of three health zones with confirmed Ebola cases, complicating efforts to find and monitor hundreds of people who have been in contact with those infected.