1.1 Acute respiratory infections

Influenza, pneumonia and other acute respiratory infections (ARIs) are often forgotten in the focus on TB, HIV/AIDS and malaria, but they rank first among infectious causes of disease worldwide:

• The average global burden of seasonal influenza alone is about 600 million cases per year, of which 3 million result in severe illness, causing between 0.25 and 0.5 million deaths (WHO, 2009a). Pandemic influenza occurs at unpredictable intervals with the emergence of new variant influenza viruses.
• The ‘swine flu’ epidemic in 2009 caused by an H1N1 virus spread rapidly to 208 countries; the speed of transmission overwhelmed the capacity for laboratory confirmation of cases, especially in low-resource countries, but clinical diagnosis suggests that several million people were symptomatically infected and at least 12 220 died (WHO, 2009b).
• Pneumonia is the largest infectious cause of death among young people globally (see Figure 1), accounting for an estimated 1.5 million deaths in children under 5 years – more than TB, HIV/AIDS and malaria combined in this age group. Pneumonia is mainly due to the bacteria Streptococcus pneumoniae and Haemophilus influenzae type b (Hib), the respiratory syncytial virus (RSV) and parainfluenza viruses, all of which also affect elderly people worldwide. A major underlying cause of susceptibility to these pathogens is inflammation of the lungs due to atmospheric pollution; this is a major problem particularly among women, children and elderly people who are persistently exposed to indoor smoke from cooking fires in poor rural communities.
• The World Health Organization (WHO) estimates that up to 18 million episodes of pneumococcal disease and around 16 million episodes of RSV disease occur globally every year.