RTI

Common Pathogens

Upper Respiratory Infections : Common Cold, Sinusitis, Pharyngitis, Epiglottitis and Laryngotracheitis

Bacteria

Group A beta hemolytic streptococci

Corynebacterium Diptheriae

Neiserria Gonorrhea

Mycoplasma pneumoniae

Haemophilus influenzae type b

Streptococcus pneumoniae

Fungus

Candida albicans

Virus

Rhinovirus

Coronavirus

Parainfluenza virus

Adenovirus

RSV

Influenza

Coxsackievirus A

EBV

CMV

HSV

Lower Respiratory Infection : Bronchitis, Bronchiolitis and Pneumonia

Bacteria

Haemophilus influenzae

Streptococcus pneumoniae

Mycoplasma pneumoniae

Staphylococcus aureus

Streptococcus pyogenes

Klebsiella pneumoniae

E. coli

Pseudomonas aeruginosa

Mycoplasma pneumoniae

Legionella spp

Mycobacterium tuberculosis

Coxiella burnetii

Chlamydia trachomatis/ psittaci/ pneumoniae

Fungus

Histoplasma capsulatum

Candida albicans

Cryptococcus neoformans

Aspergillus spp.

Virus

Parainfluenza virus

RSV

Adenovirus

HSV

Influenza

VZV

Measles

CMV

Hantavirus

Investigations

Upper RTI

(a) Common Cold
Microbiologic Diagnosis:
1. Symptoms (lack of fever combined with symptoms of localization to the nasopharynx).

(b) Sinusitis
Microbiologic Diagnosis:
1. For acute sinusitis, the diagnosis is made from clinical findings.
2. Bacterial culture: Nasal discharge (Not very helpful as the recovered organisms are generally contaminated by the resident flora from the nasal passage.)
3. In chronic sinusitis, a careful dental examination
4. Sinus x-rays
5. Antral puncture : to obtain sinusal specimens for bacterial culture (specific)

(d) Pharyngitis
Diagnosis:
1. Culture
2. Serology
3. Fluorescent antibody (Rapid diagnostic tests)
4. Latex agglutination
5. PCR

(e) Epiglottitis and Laryngotracheitis
Diagnosis:
1. Blood culture
2. Cultures : pharyngeal swabs
3. Serology : To detect a rise in antibody
4. Immunofluorescent-antibody staining (rapid diagnostic technique
5. Enzyme-linked immunosorbent assay (ELISA
6. PCR

Lower RTI

(a) Bronchitis and Bronchiolitis
Diagnosis:
1. Cultures: Sputum, Aspirations of nasopharyngeal secretions or
2. Serology : Antibody
3. Fluorescent-antibody staining
4. ELISA
5. PCR

(b) Pneumonia
Diagnosis:
1. Blood culture
2. Microscopy
3. Acid-fast stains
4. ELISA : Antigen
5. Fluorescent-antibody test
6. Serology
7. PCR

Pathogenesis

Upper Respiratory Infection

Organisms gain entry to the respiratory tract by inhalation of droplets and invade the mucosa. Epithelial destruction may ensue, along with redness, edema, hemorrhage and sometimes an exudate.

Lower Respiratory Infection

Organisms enter the distal airway by inhalation, aspiration or by hematogenous seeding. The pathogen multiplies in or on the epithelium, causing inflammation, increased mucus secretion, and impaired mucociliary function; other lung functions may also be affected. In severe bronchiolitis, inflammation and necrosis of the epithelium may block small airways leading to airway obstruction.

Management

Lower RTI

Symptomatic treatment is used for most viral infections. Bacterial pneumonias are treated with antibacterials. A polysaccharide vaccine against 23 serotypes of Streptococcus pneumoniae is recommended for individuals at high risk.

Viral infections are treated symptomatically. Streptococcal pharyngitis and epiglottitis caused by H influenzae are treated with antibacterials. Haemophilus influenzae type b vaccine is commercially available and is now a basic component of childhood immunization program.

Questions

1. Atypical lymphocytosis is most likely to be found in which of the diseases? ( Mononucleosis induced by EBV)

2. Orchitis, which may cause sterility, is a possible manifestation of which virus?(Mumps)

3.Parvovirus infection causes mild exanthem in children, is characterized by? ( Haemolytic anaemia)

4.Which of the following is transmitted by fecal- oral route, can be acquired from shellfish and often causes acute jaundice, diarrhea, and liver function abnormalities? (Hep A)

5. An experimental compound is discovered that prevents the activation of adenyl cyclase and the resulting increase in cAMP. The toxic effects of which bacteria can be prevented with this compund? ( Vibrio Cholerae)