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Brandy Darby, DVM, MPH, Diplomate, ACVPM Director, Division of Surveillance and Investigation, Office of Epidemiology, Virginia Department of HealthPublic health surveillance can be defined as the ongoing, systematic collection, analysis, and interpretation of health-related data that is essential to planning, implementing, and evaluating public health practice. As a data-driven profession, public health uses the information gleaned from surveillance efforts to inform interventions and policy.
Historically, public health surveillance began to understand the impact of infectious diseases and guided recommendations for quarantine and isolation. Subsequently, surveillance concepts have been applied to evaluate other conditions that threaten health, including chronic diseases, injury and violence, and occupational and environmental health threats. The Division of Surveillance and Investigation (DSI) within the Virginia Department of Health’s (VDH) Office of Epidemiology focuses on infectious conditions that are reportable to public health. In this article, let’s explore how public health collects surveillance data, how this data informs our response efforts, challenges that impact effective surveillance, and how VDH is working to overcome some of those challenges.
From an epidemiologic perspective, the goal of public health surveillance data is to describe a condition by person, place, and time. To prevent a disease, it is critically important to understand who is impacted, where they are being impacted, when they are impacted, and monitor how disease trends change over time. With good surveillance, we can use data to guide the development of meaningful public health interventions, and advocate for policy changes and funding to support public health’s work. Good data is collected in an organized, systematic way; standardizing how data is collected across reporting streams allows us to utilize informatics technology to automate processes and more easily analyze data to produce meaningful information.
Most disease reports to VDH are electronic laboratory reports that feed standardized data fields into the Virginia Electronic Disease Surveillance System (VEDSS) database. Other methods of disease reporting include an online portal providers can use to manually submit reports, electronic case reports, fax, and, when urgent, calling the health department. Once a report is received, local epidemiologists reach out to the case patient, or sometimes, their provider or caregiver, to collect additional information. A standardized case report form is used to collect information during the interview, including the person’s demographics (age, sex, gender, race, ethnicity, residential address), clinical signs and symptoms, illness onset, relevant diagnostic test results, relevant exposure history, and any contacts that person might have been around while infectious. Contacts of the case can then be notified. Case investigation and contact tracing disrupt chains of transmission and help to prevent the spread of the disease.
Zooming out to the larger population scale, surveillance data can be used to count cases to evaluate the burden of illness in communities and understand who is most impacted. When counting cases, standardized case definitions are used to determine if a reported case meets specific criteria to be included in case counts. Case definitions usually rely on a combination of clinical, laboratory, and epidemiologic criteria to evaluate the strength of the evidence and then classify the reported case as either a confirmed case, probable case, suspect case, or not a case. Classifying and counting cases helps us understand the ‘who,’ ‘what,’ ‘when,’ and ‘where’ of disease within a population. For nationally notifiable conditions, Virginia case data are cleaned and reported to the Centers for Disease Control and Prevention, the federal agency that leads our national public health surveillance efforts.
"Robust, flexible, surveillance systems that can seamlessly integrate laboratory, clinical, and epidemiologic data are critical to facing the next emerging public health challenge, whatever that threat might be"
Scientific advances such as genomic sequencing and bioinformatics have greatly boosted our surveillance capabilities. With genomic surveillance, we can more easily connect cases to a common exposure source or to each other, even when the epidemiologic investigation has not been able to identify a clear connection. Informatics have made it easier to share information between organizations and greatly reduced the burden of manual data entry. Still, challenges remain.
With rapidly emerging conditions, like the 2022 mpox (formerly, monkeypox) outbreak, it took time to update the standardized mpox fields in VEDSS to capture information that was important to the current situation. For example, sexual exposures were not previously recognized as an important route of transmission for mpox, but with this outbreak, it was critically important to capture sexual histories to perform effective contact tracing. While our main case database was being updated, VDH pivoted to using more flexible data collection tools, which was an effective interim solution. However, it did take time and effort to migrate that data over to VEDSS once updates were complete. Having more flexible surveillance data tools would greatly help public health stand up initial response efforts to emerging conditions.
Another challenge is that public health data is often siloed. For example, while most infectious disease case data are housed in VEDSS, vaccination data are housed in another database, the Virginia Immunization Information System (VIIS). As the COVID-19 vaccine transitioned from clinical trials to real world use, it was critically important to monitor vaccine effectiveness; we had to know the vaccination history of COVID-19 cases. This prompted the development of processes that now allow our epidemiologists to query vaccination histories in VIIS, for COVID-19 and other conditions, directly from the VEDSS system. That said, it is not always easy to crosswalk case and vaccination histories for a person, especially if key fields used for matching, like name, date of birth, or address, don’t match between systems. Enhancing system interoperability is one of the priority areas of the National Public Health Data Strategy over the coming years; this will be a huge boost to our ability to collect accurate and complete data and will better inform public health actions.
Robust, flexible, surveillance systems that can seamlessly integrate laboratory, clinical, and epidemiologic data are critical to facing the next emerging public health challenge, whatever that threat might be.
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