• Tracking Disease Trends: By monitoring diseases over time, we can see if they're increasing, decreasing, or staying the same. This helps us understand how well our control measures are working and identify any emerging patterns or changes.
• Guiding Resource Allocation: With limited resources, we need to know where they're needed most. Surveillance data helps us prioritize and direct healthcare resources to the areas and populations that need them the most.
• Evaluating Public Health Interventions: By tracking disease patterns before and after implementing public health interventions, we can determine the effectiveness of these interventions.
• Informing Public Health Policy: Surveillance data provides the evidence base for creating and implementing effective public health policies.

1. Passive Surveillance:
o    This is the most common and cost-effective method.
o    It relies on healthcare providers (doctors, nurses, hospitals) and laboratories to report cases of diseases to health authorities.
o    Think of it as: Waiting for someone to call and report a fire.
o    Pros: Cost-effective, covers a wide area.
o    Cons: Can underreport cases, as healthcare providers are often busy and might miss or forget to report.

2. Active Surveillance:
o    Health agencies actively seek out information by contacting healthcare providers, reviewing medical records, or conducting surveys.
o    Think of it as: Actively going door-to-door to check for fire hazards.
o    Pros: Provides more complete and accurate data.
o    Cons: More resource-intensive and time-consuming.

3. Sentinel Surveillance:
o    Selected healthcare facilities or groups are chosen to report all cases of specific diseases.