A cluster of people talking on social media about their mysterious rashes. A sudden die-off of birds at a nature preserve. A big bump in patients showing up to a city’s hospital emergency rooms.
These are the kinds of events that public health officials are constantly on the lookout for as they watch for new disease threats.
Health emergencies can range from widespread infectious disease outbreaks to natural disasters and even acts of terrorism. The scope, timing or unexpected nature of these events can overwhelm routine health care capacities.
I am a public health expert with a background in strengthening health systems, infectious disease surveillance and pandemic preparedness.
Rather than winging it when an unusual health event crops up, health officials take a systematic approach. There are structures in place to collect and analyze data to guide their response. Public health surveillance is foundational for figuring out what’s going on and hopefully squashing any outbreak before it spirals out of control.
Tracking day by day
Indicator-based surveillance is the routine, systematic collection of specific health data from established reporting systems. It monitors trends over time; the goal is to detect anomalies or patterns that may signal a widespread or emerging public health threat.
Hospitals are legally required to report data on admissions and positive test results for specific diseases, such as measles or polio, to local health departments. The local health officials then compile the pertinent data and share it with state or national public health agencies, such as the U.S. Centers for Disease Control and Prevention.
When doctors diagnose a positive case of influenza, for example, they report it through the National Respiratory and Enteric Virus Surveillance System, which tracks respiratory and gastrointestinal illnesses. A rise in the number of cases could be a warning sign of a new outbreak. Likewise, the National Syndromic Surveillance Program collects anonymized data from emergency departments about patients who report symptoms such as fever, cough or respiratory distress.
Public health officials keep an eye on wastewater as well. A variety of pathogens shed by infected people, who may be asymptomatic, can be identified in sewage. The CDC created the National Wastewater Surveillance System to help track the virus that causes COVID-19. Since the pandemic, it’s expanded in some areas to monitor additional pathogens, including influenza, respiratory syncytial virus (RSV) and norovirus. Wastewater surveillance adds another layer of data, allowing health officials to catch potential outbreaks in the community, even when many infected individuals show no symptoms and may not seek medical care.
Having these surveillance systems in place allows health experts to detect early signs of possible outbreaks and gives them time to plan and respond effectively.
