¶ Principles of epidemiology in public health practice

pdf copy from cdc

html version of the text from the cdc

¶ BibTeX

@article{dicker2006principles,
  title={Principles of epidemiology in public health practice; an introduction to applied epidemiology and biostatistics},
  author={Dicker, Richard C and Coronado, Fatima and Koo, Denise and Parrish, R Gibson},
  year={2006}
}

¶ My Notes on Measures of Risk

This page in particular defines and explains many terms from the epidemiological literature.

See also the cdc’s glossary

¶ Morbidity Frequency Measures

Morbidity means you’re sick.

“Incidence” is used to refer to the speed at which new cases are appearing, while prevalence counts all active cases.

Incidence proportion / Attack Rate / Risk:

Incidence rate / person-time rate:

Secondary Attack Rate:

Point prevalence:

Period prevalence:

¶ Mortality Frequency Measures

Mortality means you’re dead.

Crude death rate:

Cause-specific death rate:

Proportionate mortality:

Death-to-case ratio:

¶ Childbirth-specific terms

Neonatal mortality rate:

Postneonatal mortality rate:

Infant mortality rate:

Maternal mortality rate:

Crude birth rate:

Crude fertility rate:

Crude rate of natural increase:

¶ Measures of Association

Risk Ratio:

Rate Ratio:

Odds ratio: \(\frac{\text{exposed and diseased}\cdot \text{unexposed and no disease}}{\text{exposed and no disease}\cdot \text{unexposed and diseased}}\)

¶ Measures of Public Health Impact

Attributable proportion / attributable risk percent:

Vaccine efficacy / vaccine effectiveness:

equal to (1 - risk ratio) with unvaccinated as comparison group.

¶ Notes on Public Health Surveillance

Notifiable conditions

A notification is the reporting of certain diseases or other health-related conditions by a specific group, as specified by law, regulation, or agreement. Notifications are typically made to the state or local health agency. … When reporting is required by law, the diseases or conditions to be reported are known as notifiable diseases or conditions.

Passive surveillance

Health provider sends reports on notifiable conditions to health department, as required by law.

Active surveillance

Health department solicits reports, (such as during outbreak)

Sentinel Reporting

A pre-arranged sample of providers agree to report all cases of certain conditions.

Registries

Permanent legal records of a person’s health events. Examples: Birth, death, cancer treatment.

¶ Major health data systems

• National Notifiable Disease Surveillance System (NNDSS)
  • The list of notifiable diseases varies from state to state
  • All states typically report quarantine-worthy diseases, like cholera, plague, and yellow fever
• Chronic disease data is less timely:
  • Hospital discharge records
  • public surveys
  • National Vital Statistics System
• Risk factor data (smoking, blood pressure, etc.) relies on surveys. Examples:
  • National Health and Nutrition Examination Survey (NHANES)
    • most comprehensive, source of famous data about lead exposure and second-hand smoke
  • Behavioral Risk Factor Surveillance System (BRFSS)
  • Youth Risk Behavior Surveillance System (YRBSS)
  • National Health Interview Survey (NHIS)
  • National Household Survey on Drug Abuse
• Injuries: U.S. Consumer Product Safety Commission’s (CPSC) National Electronic Injury Surveillance System (NEISS) collects data

Here’s a list of more major health data systems

¶ Surveillance for Influenza

Flu is widespread each winter, but rarely confirmed by lab test.

Health authorities recieve reports of:

• Lab ID’d flu from nose swaps (rare)
• outbreaks of influenza-like illness
• reports from schools or businesses of excess absenteeism
• death certificates for pneumonia and flu (from some locations)
• number of flu-like patients (seen by selected physicians)
• pharmacy reports or antiviral drugs

One health department uses number of chest radiographs a mobile radiology group performs of nursing home patients as a metric.

7 Key data systems for assessing flu activity:

• 125 labs which send reports
• U.S. Influenza Sentinel Providers Surveillance Network receives reports from ~1000 providers
• 122 City Mortality Reporting System tracks pneumonia/flu deaths from 122 locales
• Each state self-asses as “No Activity,” “Sporadic,” “Local,” “Regional,” or “Widespread.”
• NNDSS labels flu-related pediatric mortality as a notifiable condition
• Emerging Infections Program keeps track of lab-confirmed flu-related pediatric hospitalizations in 11 metro areas.

¶ Sucess of NDSS mandatory reporting

• For rare and serious diseases (rabies,plague), reporting rate near 100%.
• STD and tuberculosis reporting rate also very high
• But for some diseases, reporting rate very low
  • Shigellosis and other infectious diarrheas have maybe only 1 in 20 cases reported
  • Nonbloody diarrheas maybe 1 in 40

Undoubtedly, the greatest stimulus to reporting was the prompt visit of the surveillance team for outbreak investigations and control whenever cases were reported. This simple, obvious, and direct indication that the routine weekly reports were actually seen and were a cause for public health action did more, I am sure, than the multitude of government directives which were issued. –Henderson DA. Surveillance of smallpox

¶ On biases in reporting:

First, health-care providers are more likely to report a case that results in severe illness and hospitalization than a mild case, even though a person with mild illness might be more likely to transmit infection to others because the person might not be confined at home or in the hospital. This bias results in an inflated estimate of disease severity in such measures as the death-to-case ratio.

Second, health-care providers are more likely to report cases when the disease is receiving media attention. This bias results in an underestimate of the baseline incidence of disease after media attention wanes.

Both biases were operating in 1981 during the national epidemic of tampon-associated toxic shock syndrome. Early reports indicated a death-to-case ratio much higher than the ratio determined by subsequent studies, and reported cases declined more than incident cases after the publicity waned.
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