Morbidity Rates

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Morbidity Rates

• Ashry Gad Mohamed
• Professor of Epidemiology

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Incidence

• It measures the new cases.
• It measures the force of infection or disease in
  the community.
• IR No. of new cases during a year / lacality X
  10n
• Population at risk /year/locality

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• Example
• In 1430 the number of breast cancer cases
  reported to the cancer registry in Riyadh region
  was 200. The midyear population of Riyadh region
  was four million.(2.1 males and 1.9 females)
• Calculate the incidence of breast cancer in
  Riyadh.

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Attack rate

• Acute recurrent diseases e.g. ARTI, food
  poisoning.
• Person may catch the disease more than one time.
• No. of episodes during specified period
• AR
  x k
• Population at risk/ period

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Example

• In a village of 600 persons, 1200 visits to the
  PHCC were due to flu. What is the attack rate of
  flue in the village?

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Factors affect incidence

• 1- New risk facor
• Contraceptive pills thromboembolism.
• Food additives cancer
• New agent HIV AIDS

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• 2- Changing virulence
• El-Tor vibrio cholera.
• Influenza virus mutation influenza
• Mycobacteial resistance TB

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3- Changing pattern of intervention

• Polio eradication poliomyelitis
• Chemoprophylaxis meningitis
• Environmental sanitation filth diseases

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4-Population pattern

• Aging degenerative diseases cancer

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5- Reporting

• Increase in reporting incidence
• Early stage of surveillance incidence

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6-Screening

• Screening
• early detection of cases
• Increase in incidence

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7-New diagnostics

• New diagnostic
• Increase detection of cases
• Increase in incidence

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8-Selective migration

• Floods or famines
• Decrease sanitation
• Increase susceptable
• Increase incidence

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Prevalence

• It measures the status of the disease in the
  population.
• Point prevalence
• Total cases (old new) at fixed point of time
  in place
• 
  x 10 n
• total population in the place

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• Period prevalence
• Total cases (old new) during a period of time
  in place
• 
  x 10
  n
• total population in the place

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example

• MOH conducted a survey for RVF among workers in
  slaughterhouses in Makkah. 224 seropositive
  workers were identified among 6000 workers.
• Calculate the prevalence of RVF.

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Factors affecting prevalence

• 1- Incidence
• Prevalence incidence X duration
• 2- Disease duration
• Chronic diseases are accumulating so
  increase the prevalence

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3- management programs

• If successful and curative decrease the
  prevalence.
• If only increases the survival without complete
  cure increases the prevalence

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4- Changing classification

• Blood pressure
• 140/80 Vs 160/90
• Fasting blood sugar
• 126 Vs 140

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5-Selective attrition

• If cases of the disease travel to be treated
  abroad then the prevalence decreases.

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Incidence Vs prevalence

• incidence
• Prevalence
• 
  Cure
• 
  Death
• 
  Migration

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• Time

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• Time

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Thank You