Let's spend a little time talking about surveys and surveillance, and there is so much good about surveillance. Compared to other kinds of data, surveillance data has some great advantages. First of all, it's collected in real time. It's collected as problems are arising or subsiding. There is a tendency especially with health surveillance data, for it to be collected over long periods of time so we can see what the effects were when some factor or program changed along the way. For most medical things that we are interested in such as, cases of a particular disease, surveillance data is often coming from a medical facility and it has then the potential for laboratory confirmation or confirmation by an informed medical authority so that it has high quality assurance built into it. Here's some data that was collected from Burmese refugees who had fled into Bangladesh back in 1991. This is showing young people who were buried in a graveyard, and the surveillance process in this case involved making a record of who died and how old they were and whether they were males or females. As you look at this, it's quite clear that more females seem to be being buried than males. So the fellow who collected this data, Brent Burkeholder, who worked at the Centers for Disease Control at the time, went to the nearest clinics and got some clinic surveillance data. This data from a clinic serving the same camp is actually not quite covering the same period of time. The age breakdowns aren't quite the same, but you will notice, that more male children are being brought for medical care than are female children, especially in the older age groups here. So they did a little bit of qualitative exploration and spoke with village leaders, and it quite quickly became clear that families valued their male children more than they valued their female children. At this window of time, the IMF was forcing the Government of Bangladesh to have a cost recovery component to the health care services. So these refugees had to pay to have their child treated. So this data was presented to the Ministry of Health, who then went and had conversations within the larger government, and quite quickly, the Ministry of Health agreed okay, free medical care can be provided in this camp. Within two weeks, the differential in girls going to the clinic versus boys disappeared, and the differential between boys and girls dying as a rate disappeared. So here, surveillance data was able to stop a problem as it arose. What a lovely thing. Here is some data that was collected in Mtendeli Camp, a camp full of Burmese refugees who have fled across the border into Tanzania. It is showing over a three and a half year period, all of the births that were recorded in this camp, and those births are actually broken into two categories of births, in blue are low birth weight events. That is births less than 2500 grams. In maroon are births more than 2500 grams, which are considered not low birth weight events. There were two really interesting things as you looked at the surveillance data. First was, there was quite a dramatic dip in births in late 1998. One could imagine what might have induced that but it wasn't completely clear. Secondly, over the course of time, especially over that first two years of data, the fraction of all birth events that were low birth weight events clearly diminished by a lot, by 80, 90 percent. This is a graphic showing the number of malaria cases treated in the treatment center of that camp over the exact same window of three and a half years. You'll notice quite early on, there was one month, March of 1998, the peak of this epidemic curve, where a third of the entire population was diagnosed in the clinic as having malaria. It turns out that, there was a bit of a hyperendemic chapter of malaria in 1998. That dip of births that happened about five months later is probably because women who were pregnant lost their pregnancies. It turns out that pregnant women are bitten by mosquitoes more than non-pregnant women. It turns out that women who are pregnant are very susceptible to a series of adverse consequences associated with developing malaria, including toxemia and loss of the pregnancy. Therefore, as we look at this data and see that dip, probably that's the result of the malaria hyperendemic chapter that had occurred five months before. That's interesting. But what's more interesting is, in early 1998, the NGO The International Rescue Committee in an attempt to get more women to undertake antenatal care started providing a food supplement to pregnant women as part of antenatal care. Lo and behold, in the months that follow, the fraction of all births that are low birth weight events went down dramatically. It shouldn't surprise any of us that feeding pregnant women cut down on low birth weight events. That's not very advanced science. But what is fascinating in this story is, that up until that time, for the three years before that this campaign existed, about three percent of all births were syphilis positive births. There are enormous complications, very serious complications that can arise when a woman who's syphilis positive gives birth. The child can end up becoming blind, the child can end up arriving as a stillbirth, and it seems antenatal care increased dramatically when the supplemental feeding program began. That the act of feeding pregnant women actually reduced the incidence of syphilis positive births. Who could have imagined in this camp where various campaigns had happened trying to get women to get into antenatal care, who could have imagined that the best way to control syphilis was to give a food supplement to pregnant women. This is the sort of lesson that can only be learned by surveillance data that is ongoing and collected in a systematic way, so that when changes in society occur or changes in health outcomes occur, we can try to reconstruct why did that change happen. In this case, we managed to better control syphilis by adding supplemental feeding to the suite of services in antenatal care. So here is some surveillance data associated with the last chain of transmission of Ebola in Liberia. Here, each time a case would arise, they would find out who the contacts were and visit them on a weekly basis and actually multiple times per week and take their temperature. Here they are, they're tracing these cases very, very carefully to try to control and stomp out this outbreak. This is surveillance in a really aggressive, active way. Certain really powerful things can arise from active surveillance like this.