Endogenous infection

The body’s own endogenous flora can cause infection if the organism gains access to an inappropriate area of the body. This can happen by simple mechanical transfer, for example colonic bacteria entering the female urinary tract. The non-specific host defences may be breached, for example by cutting or scratching the skin and allowing surface commensals to gain access to deeper tissues; this is frequently the aetiology of cellulitis. There may be more serious defects in host immunity owing to disease or chemotherapy, allowing normally harmless skin and bowel flora to produce invasive disease.

Airborne spread

Many respiratory tract pathogens are spread from person to person by aerosol or droplet transmission. Secretions containing the infectious agent are coughed, sneezed, or breathed out, and are then inhaled by a new victim. Some enteric viral infections may also be spread by aerosols of faeces or vomit. Environmental pathogens such as Legionella pneumophila, and zoonoses such as psittacosis, are also acquired by aerosol inhalation, while rabies virus may be inhaled in the dust from bat droppings.

Faeco-oral spread

Transmission of organisms by the faeco-oral route can occur by direct transfer (usually in small children), by contamination of clothing or household items (usually in institutions or conditions of poor hygiene), or most commonly via contaminated food or water. Human and animal faecal pathogens can get into the food supply at any stage. Raw sewage is used as fertilizer in many parts of the world, contaminating growing vegetables and fruit. Poor personal hygiene can result in contamination during production, packaging, preparation or serving of foodstuffs. In the western world, the centralization of food supply and increased processing of food has allowed the potential for relatively minor episodes of contamination to cause widely disseminated outbreaks of food-borne infection.

Table 2-3. Environmental organisms which can cause human infection

Organism	Disease (most common presentations)
Bacteria
Burkholderia pseudomallei	Melioidosis
Burkholderia cepacia	Lung infection in cystic fibrosis
Pseudomonas spp.	Various
Legionella pneumophila	Legionnaires’ disease (pneumonia)
Bacillus cereus	Gastroenteritis
Listeria monocytogenes	Various
Clostridium tetani	Tetanus
Clostridium perfringens	Gangrene, septicaemia
Mycobacteria other than tuberculosis (MOTT)	Pulmonary infections
Fungi
Candida sp.	Local and disseminated infection
Cryptococcus neoformans	Meningitis, pulmonary infection
Histoplasma capsulatum	Pulmonary infection
Coccidioides immitis	Pulmonary infection
Mucor spp.	Mucormycosis (rhinocerebral, cutaneous)
Sporothrix schenkii	Lymphocutaneous sporotrichosis
Blastomyces dermatitidis	Pulmonary infection
Aspergillus fumigatus	Pulmonary infections

Water-borne faeco-oral spread is usually the result of inadequate access to clean water and safe sewage disposal, and is common throughout the developing world. Global coverage for access to clean drinking water is 83% of the world population but global sanitation coverage is currently 58%.

Table 20-2. Aetiology of epistaxis

Local	Idiopathic
	Trauma – foreign bodies, nose-picking and nasal fractures
	Iatrogenic – surgery, intranasal steroids
	Neoplasm – nasal, paranasal sinus and nasopharyngeal tumours
General	Anticoagulants
	Coagulation disorders
	Hypertension
	Osler-Weber-Rendu syndrome (familial haemorrhagic telangiectasia)

Nose bleeds vary in severity from minor to life-threatening. Little’s area is a frequent site of nasal haemorrhage. First aid measures should be administered immediately, including compression of the anterior lower portion of the external nose, ice packs and leaning forward. The patient should be asked to avoid swallowing any blood running posteriorly. If the bleeding continues profusely then resuscitation in the form of intravenous access, fluid replacement or blood, and oxygen can be administered. If further intervention is necessary, consideration should be given to intranasal cautery of the bleeding vessel, or intranasal packing may be undertaken using a variety of commercially available nasal packs. In addition to direct treatment of the epistaxis, a cause and appropriate treatment of a cause should be sought (Table 20.2).