1. Pneumonia
Etiology
Pneumonia is an infection of the lower respiratory tract that involves the airways and parenchyma with consolidation of the alveolar spaces.
Pneumonia is general term for lung inflammation that may or may not be associated with consolidation .
Lobar pneumonia describes pneumonia localized to one or more lobes of the lung.
Atypical pneumonia describes patterns typically more diffuse or interstitial than lobes pneumonia.

2. Bronpnechoumonia refers to inflammation of the lung that is centered in the bronchioles and leads to the production of a mucopurulent exudate that obstructs some of these small airways and causes patchy consolidation of the adjacent lobules.
Interstitial pneumonitis refers to inflammation of the interstitium , which is composed of the walls of the alveoli, the alveolar sacs and ducts, and the bronchioles. Interstitial pneumonitis is characteristic of acute viral infections but also may be a chronic inflammatory or fibrosing process. Defects in host defenses increase the risk of pneumonia .
Infections agents that commonly cause community acquired pneumonia vary by age.

3. Most common causes are respiratory syncytial virus (RSV) in infants , other respiratory viruses (pa-rainfluenza viruses , influenza viruses, human metapneumovirus, adenoviruses) in children younger than 5 years old, and Mycoplasma pneumonia children older than 5 years old.
Streptococcus pneumonia is most common bacterial causes of lobar pneumonia , and occurs in children of any age outside the neonatal period. M. pneumonia and Chlamydophila pneumonia are principle causes of a typical pneumonia

4. Chlamydia trachomatis and less commonly Mycomplasma hominis , Ureaplasma uealyticum , and cytomegalovirus (CMV) cause a similar respiratory syndrome in infants 1 to 3 months of age with subacute onset of an afebrile pneumonia cough and hyperinflation are the predominant sign .
These infections are difficult to diagnose and to distinguish from each other.
Additional agents occasionally causes pneumonia .
Sever acute respiratory syndrome (SARS) is due to SARS –associated coronavirus (SARS-COV) . Avian influenza (bird flu) is a highly contagious viral disease of poultry and other birds caused by influenza A (H5N1).

5. There were outbreaks among humans in south East Asia in 1977 and 2003 to 2004 with high mortality rates. A novel influenza A(H1N1) of swine origin began circulating in Other etiologic agents include mycobacterium tuberculosis .
Cause of pneumonia in immunocompromised persons include gram-negative enteric bacteria, mycobacteria (M.avium complex), fungi (aspergillosis), viruses (CMV) and Pnemocystis jiroveci (cariniii).
Pneumonia in patients with cystic fibrosis usually is caused by Staphylococcus aureus in infancy and pseudomonas aerougionsa in older patients.

6. EPIDEMIOLOGY
Immunizations have had a greet impact on the incidence of pneumonia caused by pertussis , diphtheria , measles. Haemophilus influenza type b , and S. pneumonia (BCG) bacille Calmette-Gurein for tuberculosis also has had an impact .
Risk factors for lower respiratory tract infections include gastroesophageal reflux, neurologic impairment (aspiration ), immunocompromised state , anatomic abnormalities of the respiratory tract, and hospitalization , especially in an intensive care unit.

7. CLINICAL MANIFESTATIONS
Age is determinant in the clinical manifestations of pneumonia . Neonates may have fever or hypoxia only , with subtle or absent physical examination findings. With a young infant , apnea may be the first sign of pneumonia . Fever , chills, tachypnea, cough, malaise, pleuritic chest pain, retractions , and apprehension , because of difficulty breathing or shortness of breath , are common in older infants and children.
Physical examination findings cannot reliably distinguish viral and bacterial pneumonia, but complete physical examinations may help indentify findings to suggest an etiology.

8. CLINICAL MANIFESTATIONS
In general viral pneumonia are associated more often with cough , wheezing , or stridor, fever is less prominent than bacterial pneumonia. Mucosal congestion and upper respiratory inflammation suggest a viral infection .
Bacterial pneumonias typically are associated with higher fever , chills, cough , dyspnea, and auscultatory findings of lung consolidation . A typical pneumonia in young infants as characterized by tachypnea, cough, crackles on auscultation , and concomitant (Chlamydial ) conjunctivitis (infants) may be present. Other signs of respiratory distress include nasal flaring, intercostal and subcostal retractions, and grunting .

9. CLINICAL MANIFESTATIONS
Dullness to percussion may be due to lobar or segmental infiltrates or pleural fluid .Auscultation may be normal in early or very focal pneumonia, but the presence of localized crackles, rhonchi , and wheezes to detect pneumonia.
Distant breath sounds may indicate a large , poorly ventilated area of consolidation or pleural fluid.

10. LABORATORY AND IMAGING STUDIES
The white blood cell (WBC) count with viral pneumonia is often normal or mildly elevated , with a predominance of lymphocytes, whereas with bacterial pneumonia . The WBC count is elevated (> 2000 /mm3) with a predominance of neutrophils. Mild eosinophilia is characteristic of infants C. trachomatis pneumonia .
Blood cultures should be performed on hospitalized children . Blood cultures are positive in 10% to 20% of bacterial pneumonia .
Viral respiratory pathogens can be diagnosed using polymerase chain reaction (PCK) or rapid viral antigen detection but neither rule out concomitant bacterial pneumonia .

11. LABORATORY AND IMAGING STUDIES
Mycloasma pneumonia should be suspected if cold agglutinins are present in peripheral blood samples and can be confirmed by Mycomplasma PCR. CMV and entero- virus can be cultured from nasopharynx , urine , or bronchoalveolar lavage fluid. The diagnosis of M. tuberculosis is established by tuberculin skin test, serum interferon- gamma release assay , or analysis of sputum or gastric aspiratory by culture , antigen detection or PCR. Other investigation like bronchoscopy with bronchoal- veolar lavage and brush mucosal biopsy , needle aspiration of the lung & open lung biopsy are method of obtaining material for microbiologic diagnosis in special cases.

12. LABORATORY AND IMAGING STUDIES
When there is a pleural effusion or empyema, a thoracentesis to obtain pleural fluid can be diagnostic and therapeutic.
Frontal and lateral radiograph are required to localized disease & adequately visualize retrocardiac infiltrates.
Bacterial pneumonia shows lobar consolidation , or around pneumonia , with pleural effusion in 10 % to 30% of cases. Viral pneumonia shows diffuse, streaky infiltrate of bronchopneumonia and hyperinflation. Atypical pneumonia , such as with Mycomplasma , pneumonia and Chlamydia pneumonia , shows increased interstitial marking or bronchopneumonia. Chest radio graph may be normal in early pneumonia .

13. LABORATORY AND IMAGING STUDIES
Hilar lymphadenopathy may be a sign of tuberculosis, histoplamosis or an underlying malignant neoplasm. Computed to tomography (CT) is used to evaluate serious disease , pleural abscess, bronchiectasis, and effusion.

14. TREATMENT
Most cases of pneumonia in healthy children can be managed on an outpatient basis.
However children with hypoxemia , inability to maintain adequate hydration , or moderate to severe respiratory distress should be hospitalized .hospitalization should be considered in infants under 6 months with suspected bacterial pneumonia , or when concern exist about a family’s ability to care for the child and to asses symptoms progression. Because virus cause most community -acquired pneumonias in young children , not all children require empirical antibiotic treatment for pneumonia .

15. COMPLICATIONS AND PROGNOSIS
Bacterial pneumonias frequently cause inflammatory fluid to collect in the adjacent space , causing a parapneumonic effusion or , if grossly purulent, an empyema. Large effusion require drainage. Air dissection within tissue result in a pneumatocele. Scarring of the airways and lung tissue resulting in bronchiectasis and increased risk for recurrent infection . Pneumonia that causes necrosis of lung tissue may lead to a lung abscess . Chest radiograph or CT scan reveals a cavitary lesion with air fluid level , surrounded by parenchymal inflammation.
Most children recover from pneumonia rapidly & completely , although radiographic abnormalities may take

16. COMPLICATIONS AND PROGNOSIS
6 to 8 weeks to return to normal.
Sever adenovirus pneumonia may result in bronchiolitis obliterans a subacute inflammatory process in which the small airways are replaced by scar tissue, resulting in a reduction in lungs volume and lung compliance . Unilateral hyper lucent lung. Or Swyer–James syndrome , is a focal sequela of severe necrotizing pneumonia in which all part of a lung has increased translucency radiographicially . It is due to adenoviruse type 21.

17. PREVENTION
Annual influenza vaccine is recommended for all children over 6 months of age .
Children hood vaccination with conjugate vaccines for H influenza type b & streptococcus pneumonia has greatly diminished the incidence of these pneumonias. The severity of RSV infections can be reduced by use of palivizumab in high risk patients.