Health Hygiene & Sanitation

Lesson 36 : Prevention Of Respiratory Infections


Influenza is an acute respiratory tract infection caused by influenza virus either A, B or C. All known pandemics were caused by influenza A strains. The disease is characterized by sudden onset of chills, malaise, fever, muscular pains and cough.

Agent Factors:

  • Agent: Influenza viruses belong to the family ‘Orthomyxoviridae’. There are three viral subtypes, namely influenza type A, type B and type C. Of these type A and B cause epidemics.

  • Reservoir of Infection: Major reservoir of influenza virus exists in animals and birds.

  • Source of Infection: Usually a case or subclinical case. The secretions of the respiratory tract are infective.

  • Period of Infectivity: Virus is present in the nasopharynx from 1 to 2 days before and 1 to 2 days after onset of symptoms.

Host Factors:

  • Age and Sex: Influenza affects all ages and both sexes,

  • Human Mobility: This is an important factor in the spread of infection.

  • Immunity: Immunity to influenza is subtype - specific. Antibodies against Hemagglutinin A and Neuraminidase A are important in immunity to influenza.

Environmental Factors:

  • Season: The epidemics usually occurs in winter months in Northern Hemisphere and in winter or rainy season in the Southern Hemisphere. In India, epidemics have often occurred in summer.

  • Over Crowding: Enhances transmission. The attack rates are high in close population groups, e.g., schools, institutions, ships. Etc

Mode of Transmission:

Influenza is spread mainly from person to person by droplet infection or droplet nuclei created by sneezing, coughing, talking The portal of entry of the virus is the respiratory tract.

Incubation Period: 18 to 72 hours


Good ventilation of public buildings, avoidance of crowded places epidemics, encouraging sufferers to cover their faces with a handkerchief while coughing and sneezing, and to stay at home at the first sign of the disease.

Influenza Vaccines:

  • Killed vaccine
  • ‘LIVE’ attenuated vaccine
  • Newer vaccines
Last modified: Thursday, 26 April 2012, 12:54 PM