Respiratory tract infections (RTI's) can be divided into upper RTI’s, including tonsillitis, sinusitis and otitis media, and lower RTI’s, including bronchitis and pneumonia. Bacterial infections are usually preceded by viral respiratory tract infections. RTI’s are usually spread directly by droplet or airborne transmission. Washing hands is considered to be an effective preventive measure.

Tonsillitis is an acute inflammation of the tonsils. The infection is usually caused by Streptococcus pyogenes and characterised by a sore throat and painful swallowing. Fever, malaise and headache are common.

Otitis media is a bacterial infection of the middle ear. Acute otitis media is most common in young children, where it is often caused by Streptococcus pneumoniae, Hemophilus influenzae and Staphylococcus aureus. Symptoms are persistent and may include severe pain, fever, nausea, vomiting and diarrhoea.

Sinusitis is an inflammation of the paranasal sinuses' cell lining, the paranasal sinuses being the air cavities in the skull surrounding the nose. Sinusitis can be caused by viruses, bacteria or fungi. An acute bacterial sinusitis is usually preceded by a viral RTI, e. g. a common cold, paving the way for a superinfection with bacteria like Haemophilus influenzae, streptococci, or staphylococci. Symptoms include severe feelings of pressure and pain in the facial area, the teeth and forehead, nasal congestion with thick, yellow-green mucous discharge and fever. Early diagnosis and effective treatment of acute sinusitis are essential for the prevention of chronic sinusitis and associated complications.

Acute bronchitis is an inflammation of the mucous membrane of the bronchial tree. Primary pathogens are mainly viruses, i.e. common cold, but bacteria such as Haemophilus influenzae and Streptococcus pneumoniae may cause secondary infection. Symptoms of bacterial bronchitis are coughing, purulent expectoration and a dry, coarse rattling sound in the bronchi. The infection is generally self-limited with eventual complete healing. Still, bronchitis may be serious in debilitated patients and those with chronic lung and heart disease.

Frequent infections can result in chronic bronchitis, which has become a major health issue, especially in the elderly. The acute exacerbation of chronic bronchitis (AECB) can be triggered by infection with Haemophilus influenzae, Streptococcus pneumoniae and Moraxella catarrhalis.

Pneumonia is the inflammation of the lung parenchyma (special tissue in lungs). Pneumonia is not only the first common cause of death from infection but also the most frequent lethal hospital-acquired infection. The different types of pneumonia can be characterised by the disease-causing pathogens. In adults typical community-acquired pneumonia is mostly caused by bacteria such as Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis and Staphylococcus aureus. Atypical pneumonia is mostly caused by Mycoplasma pneumonia, Chlamydia pneumoniae, bacteria-like organisms, and Legionella pneumophilia (a bacterium living mainly in warm water reservoirs) or viruses.