Respiratory Infections

Respiratory tract infections are typically divided into upper and lower respiratory tract infections which occur mainly in the nose, throat affecting upper respiratory system, windpipe, airways and lungs affecting lower respiratory system. From clinical point of view; symptoms such as nasal obstruction, nasal discharge, sore throat, cough, irritability occur as upper respiratory tract infections, symptoms such as bronchitis and pneumonia occur as lower tract infections.

When there is no adequate treatment, bronchitis, pneumonia, emphysema, asthma and bronchiectasis may occur. Respiratory infections include a diverse group of bacterial, viral and fungal infections which makes the respiratory diseases are very contagious which can spread through different routes of transmission, including contact, droplet, and airborne. Viral causative agents of respiratory infections include rhinovirus, adenovirus, Coxsackievirus, parainfluenza virus, influenza virus, respiratory syncytial virus and human metapneumovirus. Bacterial causative agents of respiratory infections include Streptococcus, Chlamydia, Mycoplasma and Gonococcus. Fungal causative agents of respiratory infections include opportunistic fungal pathogens such as Candida and Aspergillus [1,2,3].

Among these infections; pneumonia, Legionnaires’ disease and asthma are the most dangerous and common ones. Pneumonia, caused by Chlamydophila pneumoniae, is a worldwide occurring health problem. Only in the United States, 300.000 cases are reported every year. Studies implicate that prevalence is much higher in developing countries [4] C. pneumoniae may colonize in the patient’s nose, throat, windpipe and lungs. Bacteria is transmitted through hand contact, inhalation and environmental surfaces which are generated when infected person who sneeze, sick cough in close contact with heathy individual. Bacteria requires long incubation time to infect others. The transmission of the disease is more common in crowded public areas such as hospitals, schools, prisons, dormitories etc. [5,6] L. pneumophila is the causative agent of legionellosis, which refers to Legionnaires’ disease and pontiac fever [7]. L. pneumophila is a gram negative, aerobic, flagellated bacterium of the genus Legionella. It has a unique lipopolysaccharide structure in outer side of the outer membrane, which leads to weaker colorization with gram dye compared to other gram-negative bacteria [8].

Legionnaires’ disease is a bronchopneumonia with an attack rate of 2-7% and 2-10 days long incubation period. In contrast, pontiac fever is an acute disease with an attack rate of 95-100% and 36 hours long incubation period. 1-3% of community acquired pneumonias, 13% of hospital acquired pneumonias and 26% of atypical pneumonias are caused by L. pneumophila [9]. M. pneumoniae infections with an incubation period of 2-3 weeks, occur worldwide without relation to season or geography and can cause epidemics in every 4-8 years [10].


  1. Mahony, James B. “Detection of respiratory viruses by molecular methods.” Clinical microbiology reviews 21.4 (2008): 716-747.
  2. Bulla, A., and K. L. Hitze. “Acute respiratory infections: a review.” Bulletin of the World Health Organization 56.3 (1978): 481
  3. Kon, Kateryna, and Mahendra Rai, eds. The Microbiology of Respiratory System Infections. Vol. 1. Academic Press, 2016.
  4. Kuo CC, Jackson LA, Campbell LA, Grayston JT. Chlamydia pneumoniae (TWAR). Clinical Microbiology Reviews. 1995;8(4):451-461.
  5. Conklin, L., Adjemian, J., Loo, J., Mandal, S., Davis, C., Investigation of a Chlamydia pneumoniae Outbreak in a Federal Correctional Facility in Texas
  6. Kevin A. Fajardo, Shauna C. Zorich, Jameson D. Voss, Jeffrey W. Thervil., Pneumonia Outbreak Caused by Chlamydophila pneumoniae among US Air Force Academy Cadets, Colorado, Emerging Infectious Diseases Vol. 21, No. 6, June 2015
  7. Cunha B.A., Burillo A., Bouze E. Legionnaries’ Disease. Lancet. 2016 Jan 23.387 (10016):376-85.
  8. Mauchline W.S., Araujo R., Wait R., Dowsett A.B., Dennis P.J., Keevil C.W. Physiology and morphology of L. pneumophila in continuous culture at low oxygen concentration. Journal of General Microbiology (1992). Nov; 138(11):2371-80.
  9. Doebbeling B.N., Wenzel R.P. The epidemiology of L. pneumophila infections. Seminars in Respiratory Infections. 1987 Dec;2(4):206-21.Etten, J. Van (1989). “A phylogenetic analysis of the mycoplasmas: basis for their classification”. J. Bacteriol 171: 6455–6467
  10. Atkinson, T. P., Balish, M. F. and Waites, K. B. (2008), Epidemiology, clinical manifestations, pathogenesis and laboratory detection of Mycoplasma pneumoniae infections. FEMS Microbiology Reviews, 32: 956–973. doi: 10.1111/j.1574-6976.2008.00129.x

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