Active Surveillance

Active surveillance is a proactive approach to infectious disease monitoring in which public health authorities initiate direct efforts to identify cases, rather than relying on routine reports from healthcare providers or laboratories.

This often involves systematically contacting healthcare facilities, reviewing medical records, interviewing patients or clinicians, or conducting targeted screening and diagnostic testing in high-risk populations.

Active surveillance is more resource-intensive than passive surveillance but offers greater accuracy, completeness, and timeliness—especially during outbreaks, in sentinel sites, or when monitoring for specific diseases that are underreported or of high consequence.

When active surveillance is used

It is particularly valuable when early detection is critical to containment, when asymptomatic or mild cases may be missed in routine care, or when public health needs precise estimates of disease burden or intervention impact.

Key features of active surveillance

Active systems involve dedicated outreach and systematic data collection by public health authorities.

Common active surveillance activities

• Phone or onsite follow-up with healthcare providers
• Chart reviews and retrospective case finding
• Community-based screening or testing
• Contact tracing and case finding in outbreaks
• Surveys in high-risk populations
• Enhanced case confirmation through lab testing

Settings ideal for active surveillance

• Long-term care facilities
• Outbreak response teams
• Vaccination monitoring programs
• Sentinel hospitals or clinics
• Refugee camps or high-density housing

These settings benefit from high-intensity data collection efforts to detect and respond to threats quickly.

Examples of active surveillance in action

• Salmonella outbreak investigations
• Strep A screening in long-term care settings
• Vaccine safety follow-up cohorts

Why active surveillance matters

• Detects underreported or asymptomatic cases
• Improves accuracy of disease burden estimates
• Enables faster and more targeted public health response

Case studies: targeted active surveillance

Salmonella and foodborne outbreak response

Following detection of a lab cluster, investigators actively interview patients and trace exposures.

• Collect food histories and restaurant visit data
• Test leftover food and kitchen environments
• Identify unreported or misdiagnosed cases

Group A Strep in long-term care facilities

In response to invasive cases, public health teams may conduct facility-wide swabbing and case review.

• Screen residents and staff for colonization
• Evaluate antibiotic prophylaxis practices
• Implement enhanced infection control measures

Vaccine safety and effectiveness monitoring

Active systems follow cohorts of vaccinated individuals and monitor for outcomes over time.

• Link to clinical and laboratory data systems
• Assess adverse events and real-world effectiveness
• Inform regulatory and public health guidance

Targeted screening in high-risk communities

Active surveillance helps detect disease in populations with limited healthcare access.

• Mobile testing for tuberculosis or HIV
• STI screening in shelters and jails
• COVID-19 testing in essential workers

Active tracing of imported disease cases

For diseases like Ebola or measles, public health agencies actively monitor travelers and close contacts.

Advantages and limitations of active surveillance

• High-quality, timely, and complete data
• Flexible for targeted or time-limited investigations
• Resource-intensive and often not scalable nationwide

Integration and sustainability

• Use active surveillance to validate passive reports
• Embed within sentinel networks for continuity
• Train surge teams for emergency deployment

Future directions for active surveillance

Strengthening rapid response and targeted data collection

• Leverage electronic health records for real-time case finding
• Use mobile data collection apps in field investigations
• Integrate with genomic sequencing and digital contact tracing
• Develop protocols for rapid deployment in emergencies
• Support international collaboration for cross-border surveillance