**5. Etiology**

bacterial, viral, and less commonly fungal [3]. In the pediatric age group, pneumonia may additionally be classified as non-severe, severe, or very severe depending on the signs and

Hospital-acquired pneumonia (HAP) or nosocomial pneumonia refers to any pneumonia contracted by a patient in a hospital at least 48–72 h after being admitted. Community-acquired pneumonia (CAP) is defined as pneumonia acquired outside a hospital or a long-term care facility. It occurs within 48 h of hospital admission or in a patient presenting with pneumonia who does not have any of the characteristics of healthcare-associated pneumonia. The nosocomial pneumonia, which is associated with mechanical ventilation for a duration of more than 48 h, is termed as ventilator-associated pneumonia (VAP), whereas the healthcare-associated pneumonia is defined as the pneumonia occurring in non-hospitalized patients having con-

From 1930s, prior to the discovery of antibiotic, till date pneumonia remains the major cause of death among all age groups accounting for four million deaths annually. The rate of death is highest among children aged less than 5 years worldwide [5]. According to a study conducted by Farooqui et al. [6], 3.6 million (3.3–3.9 million) episodes of severe pneumonia and 0.35 million (0.31–0.40 million) all-cause pneumonia deaths occurred in children younger than 5 years in India. Furthermore, 0.56 million (0.49–0.64 million) severe episodes of pneumococcal pneumonia and 105,000 (92,000–119,000) pneumococcal deaths occurred in India. According to American Thoracic Society/Infectious Diseases Society of America (ATS/IDSA), 2005, HAP had a crude mortality rate of 30–70% with an estimated attributable mortality rate to pneumonia between 27 and 50%. According to some estimates, VAP contributes up to 50–85% of all cases of nosocomial pneumonia [7, 8]. Furthermore, it mainly occurs in intensive care unit (ICU) patients where they most often require ventilator support, amounting to 9–27% of all mechanically ventilated patients [8]. It is estimated that four million cases of CAP occur annually in the United States, of which 20–25% are severe enough to warrant hospitalization [9]. Pneumonia is responsible for about 1.6 million deaths among children aged <5 years in Africa and South-East Asia regions [10, 11]. HAP and VAP are important causes of mortality and

morbidity, which continue to baffle the treating physicians in today's era of MDR.

Pneumonia is one of the most common causes of economic burden across the globe involving great exploitation of health resources. World Health Organization (WHO) has indicated

symptoms [4].

126 Contemporary Topics of Pneumonia

**2. Definitions**

tact with the healthcare system.

**3. Epidemiology**

**4. Economic burden**

The etiology of pneumonia in high-income countries is different than in low-income countries [12, 13]. It has been reported that viruses contribute to 30–67% cases of CAP in developed countries and are more frequently identified in children aged less than 1 year than in those aged above 2 years [12]. Bacteria are more frequently identified with increasing age, resulting in mixed infections being less common with age [12].

Respiratory syncytial virus (RSV) is the prime cause of viral pneumonia in children admitted to hospital in developing countries, followed by influenza A and B, parainfluenza, human metapneumovirus, and adenovirus [13]. The bacterial pathogens causing pneumonia include *Pseudomonas aeruginosa, Haemophilus influenza* type b, *Acinetobacter baumannii, Klebsiella pneumoniae, Escherichia coli, Staphylococcus aureus*, methicillin-resistant *S. aureus* (MRSA), and *Streptococcus pneumoniae* [8, 14, 15].
