**3.1. Pneumonia in children**

The World Health Organization (WHO) established the Child Health Epidemiology Reference Group (CHERG) to monitor the incidence of childhood [23]. In 2000, CHERG compiled pneumonia statistics in children under age 5. It was found that there were 150 million new cases of pneumonia in children under 5. Of these, approximately 4 million occurred in developed countries, while the majority occurred in developing nations [24]. Hospitalization rates for pneumonia were approximately 9%. More than half of all worldwide cases of childhood pneumonia occurred in just five countries: India, China, Pakistan, Indonesia, Nigeria and Bangladesh. Europe had the lowest rate (0.06 episodes per child-year), while Southeast Asia and Africa had the highest overall incidence rates (0.36 and 0.33 episodes per child-year, respectively). Factors that increased the risk of developing childhood pneumonia included low birth weight, malnutrition, crowded living quarters, indoor air pollution, insufficient breast feeding, and lack of vaccinations. Other possible contributing factors included pre-existing medical conditions such as asthma, and annual rainfall levels. Also, parents who smoked and lack of parent education [25].

#### **3.2. Pneumonia in adults**

Pneumonia is a serious concern in adults and viruses cause 15–30% of cases in immunocompetent adults hospitalized with pneumonia [26]. Increased rates of pneumonia-associated hospitalizations have been reported in the United States, Denmark, United Kingdom, and the Netherlands. In 2010, approximately 1.1 million patients in the USA were hospitalized for pneumonia with an average length of hospital stay 5.2 days [27]. In the UK, the number of hospitalizations due to pneumonia increased by 34% during the period from 1997 to 2005. This was particularly notable in older adults. Approximately 26,000 people died from pneumonia and influenza in England and Wales in 2013 according to national statistics. Contributing factors may be due to other chronic diseases such as heart disease, diabetes, and immunocompromised patients [28].
