Communicable Diseases and Infection Control

Communicable Diseases

• Communicable diseases are illnesses caused by infectious agents or their products that can be transmitted from an infected person, animal, or inanimate reservoir to a susceptible host.
• Infection control requires both individual and community measures.

R-naught (R0)

• R0 is the basic reproduction number, which measures the transmissibility of infectious agents.
• R0 indicates if a disease will spread or decline within a community and how far and how rapidly transmission will occur.
• R0 values:
  • Less than 1: the disease will not spread and will eventually die out.
  • 1: the disease will remain stable in the community but will not cause an epidemic.
  • Greater than 1: the disease will spread and may cause an epidemic.

Control of Communicable Diseases

• Mastering infection control requires a thorough understanding of various infectious diseases.
• Disrupting the propagation of an infectious disease outbreak often only requires understanding how it is transmitted.

HIV/AIDS

• HIV is a retrovirus that infects various cells of the immune system.
• HIV is transmitted through sexual contact, exposure to blood and blood products, childbirth, and breastfeeding.
• Prevention strategies:
  • Education, awareness, and health promotion
  • Post-exposure prophylaxis (chemoprevention)
  • Building health care infrastructure and capacity globally
  • Preventing infected mothers from transmitting the disease to their babies during delivery or through breastfeeding
  • Screening blood/transplant organs of donors
  • Safe sex
• Primary prevention of perinatal transmission:
  • Counseling and testing of pregnant women
  • Adhering to HIV treatment regimen throughout pregnancy and childbirth
  • Giving antiretroviral prophylaxis to the baby after birth
• Post-exposure prophylaxis (PEP):
  • Taking medicine to prevent HIV after exposure (e.g., needle stick injuries)
  • Must be started within 72 hours after exposure and taken daily for 28 days
• Secondary prevention:
  • HIV testing and strengthening local surveillance
  • Improving early diagnosis and access to care
• Tertiary prevention:
  • Treatment with highly active antiretroviral therapy (HAART) or antiretroviral therapy (ART)

Tuberculosis (TB)

• Caused by Mycobacteria (M. tuberculosis in humans and M. bovis in cattle)
• Spread through airborne droplets from people with pulmonary or laryngeal TB
• Stages of TB:
  • Primary TB (exposure): when a person has been in contact with someone who has TB
  • Latent TB infection: the disease remains in a quiet (dormant) state, but never resolves completely
  • TB disease: the person has signs and symptoms of an active infection
• TB interplay of the host and the organism during the initial infection is influenced by multiple factors, including age, immune status, amount of inoculum, nutritional status, and comorbidities
• Untreated, about half of the patients with active TB will die of the disease within 2 years, but modern chemotherapy almost always results in a cure

Malaria

• Primary prevention:
  • Strengthened vector control activities
  • Use of insecticide-impregnated bed nets and curtains, residual house spraying
• Secondary prevention:
  • Case finding
  • Early diagnosis
  • Prompt malaria diagnosis: rapid diagnostic tests (RDTs)
  • Confirmation of diagnosis is by demonstrating malaria parasites on blood smears
• Tertiary prevention:
  • Treatment with combination therapy to reduce resistance
  • Treatment regimens vary by region, depending on drug resistance patterns and potential drug options