Attachment

Once you suspect there is an outbreak, you need to find out far more than the number of cases. If the disease might spread fast, you need information such as exactly who was infected, the locations where they might have picked up the pathogen, and the people to whom they may have passed it. Gathering this information can be a time-consuming task, but it's an essential step in disease surveillance, and one of the many reasons that health systems need to be well funded and staffed. Clinics and hospitals are primary sources of information about the diseases that are passing through a community, but they aren't the only ones. After all, they see only a small fraction of what's going on in the community. Some people who are infected don't feel sick enough to bother going to the doctor, particularly if getting to the clinic is expensive or timeconsuming, as it is for many people in low- and middle-income countries. Others don't have any reason to see a doctor, because they don't feel the least bit sick. And some diseases spread so fast that it's a bad bet to wait for infected people to show up at the clinic. By the time you notice a jump in cases, it may be too late to stop a big outbreak. That's why, in addition to monitoring the people who come to clinics and hospitals, it also helps to go looking for known diseases by meeting potential patients where they are. That's called active disease surveillance, and a great example is the outreach done by workers in polio campaigns. They go on rounds in the community not only to vaccinate children but also to be alert for kids with polio symptoms, such as unusually weak leg muscles or leg paralysis that can't otherwise be explained. And polio surveillance teams can often do double duty, as they did during the Ebola epidemic of 2014-15 in West Africa, when they were trained to watch for telltale signs of Ebola as well as polio.