“Many people do not realize that they are infected with Zika. Only approximately 20% of people infected with Zika even have symptoms. Those who do have symptoms may mistake Zika infection for a case of the flu or standard “pink eye.” Many may not even go see a doctor. Even when Zika is suspected, a doctor may not check laboratory tests to confirm. Even if the doctor finds a positive test, the doctor has to report the case to local, state, or federal public health officials.
“Therefore, when you hear of reported Zika cases in the news, you may be seeing just the tip of the iceberg. This is an inherent problem with passive disease surveillance. Disease surveillance is following the incidence (the number of new cases over time) and prevalence (the percentage of the population that has the disease at a given time) of a disease. Passive surveillance means that you wait for people to tell you when they find newly identified disease cases.
“By contrast, active disease surveillance involves making efforts to search for cases. Now, there are different degrees of active surveillance. Active Zika surveillance can range from more aggressively telling to doctors to be on the lookout for Zika and then requiring that report all possible cases to searching medical records for cases that may be suspicious for Zika to routinely testing people for Zika even if they don’t have any symptoms. The aggressive active surveillance is, the more accurate the tracking of Zika is, but also the more expensive and time-intensive. For instance, regularly testing all people for Zika every week would give us a much better idea of where Zika is spreading but would probably cost far too much, be very inconvenient, and meet a lot of resistance.
“Disease surveillance can vary based on when and where you look for cases. For instance, looking for cases can be easier in larger cities where there are more people, facilities, testing equipment and laboratories, and communications channels. In more remote or poorer areas (even in large cities), the lack of such resources can lead to less or even no reporting of disease cases. This is why diseases can “hide out” and continue to spread to the point that the diseases are uncontrollable even in less remote and richer areas.
“Without good disease surveillance, it can be difficult to know how best to respond to a disease in the most efficient manner. For instance, Miami, Florida, is now spraying insecticide in attempt to control the mosquito population because now well over a dozen cases of Zika (caught from mosquitoes) have been reported. But where else do we need aggressive spraying. Waiting until you hear about cases in your neighborhood may be too late. For the Zika epidemic, tracking the following in a more active manner would be helpful:
• Zika cases: where, when, and who
• Zika disease outcomes such as birth defects and Gullain Barre Syndrome
• Mosquito population: what types of mosquitoes are where, where are they breeding, and which may be carrying the Zika virus
• Zika prevention and control measures: where and when are mosquito control, Zika testing, and other measures occurring
“The challenge is that surveillance, especially active surveillance, costs money, and to date Zika funding is still under debate in Congress and the Senate. Building and running the infrastructure and information systems that can gather, store, analyze, and communicate the appropriate information is no small task. Despite the stalling in funding decisions, the Centers for Disease Control and Prevention (CDC) recently awarded over $16 million to 40 different states and territories to build and run surveillance systems that track birth defects from the Zika virus. The awards range from $200,000 to $720,000.”