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Colds are always caused by a viral infection, most commonly a rhinovirus, coronavirus, adenovirus or other virus. Children have about 5-7 colds per year while adults have about 2-3 per year. Symptoms commonly begin about one day after exposure, are most severe 2-4 days after onset, and often last for 1-2 weeks.

In Aotearoa and in the UK, about 20% of people with a cold visit their doctor and of these only half expect to be prescribed an antibiotic. Nasal mucus commonly is clear and watery in the early days, and becomes brown, green or yellow and sticky later. The change in the colour and consistency is not an indication that a bacterial infection is complicating the cold, and is not a reason for antibiotic treatment.

Otitis media is a common illness in young children, most commonly caused by Streptococcus pneumoniae, Haemophilus influenzae or Moraxella cartarrhalis infection of middle ear fluid, which may have accumulated as a consequence of eustachian tube blockage secondary to a viral upper respiratory tract infection. Fever, ear pain, a bulging tympanic membrane and otorrhoea are the typical features. Diagnostic accuracy is increased by use of pneumatic otoscopy to detect the degree of mobility of the tympanic membrane, to supplement assessments of its colour, position and translucency.

The majority of children with otitis media do not require antibiotic treatment. Amoxicillin 15mg/kg TID for seven days is recommended for children with otitis media who have systemic symptoms, and for those who are less than six months or are aged less than two years and have severe or bilateral otitis media, and for those who have not improved after 48 hours of watchful waiting. The dose of amoxicillin may be doubled in those who have failed to respond to usual treatment or who appear to have an unusually severe illness.

Cough is a common feature of many upper respiratory tract infections: colds, sore throat, bronchitis. It is a reflex action to clear the airways of mucus, irritants, and foreign particles. It can arise from various causes including infections, allergies, asthma, postnasal drip, or gastroesophageal reflux disease (GERD). Acute coughs are most commonly linked to viral upper respiratory tract infections, such as the common cold or influenza. When caused by bacterial infections such as Bordetella pertussis (whooping cough) or Mycoplasma pneumoniae, the cough can be more prolonged and severe.



Bacterial infections of the lower respiratory tract, such as pneumonia or bronchitis, can also result in cough. These infections may manifest with additional symptoms such as fever, chest pain, and sputum production. It's important to distinguish between viral and bacterial causes, as the treatment approach varies.


Antibiotics target bacterial infections and have no effect on viruses. Therefore, a cough caused by a viral infection should not be treated with antibiotics. Over-prescribing or misuse of antibiotics can lead to antibiotic resistance, a significant global health concern.

When a cough is determined to be caused by a bacterial infection, appropriate antibiotic therapy can be beneficial. However, many acute coughs, especially those associated with the common cold or flu, are viral in origin. In such cases, antibiotics are not effective and their use can be more harmful than beneficial.

Antibiotic resistance is an inevitable consequence of antibiotic use. Exposure to antibiotic treatment creates a selective pressure that favours the survival and proliferation of resistant mutants. The speed with which this process occurs varies with regard to the antibiotic, the bacterial species, and the mode of treatment.

Ciprofloxacin, and other fluoroquinolones, suffer from the disadvantage that a single minor change in a bacterium’s genome can render that bacterium completely resistant to all fluoroquinolones. Not surprisingly, resistance to ciprofloxacin in Neisseria gonorrhoea reached rates of 90% in many nations within a decade of the widespread use of ciprofloxacin as treatment for gonorrhoea. Widespread use of fluoroquinolones as treatment for urinary tract infections is strongly associated with ciprofloxacin resistance in E. coli.

Topical treatment, in which the bacteria on the skin may be exposed to relatively low concentrations of the antibiotic present in the ointment or cream, is well known as a very effective way to promote antibiotic resistance. The extremely high rates of dispensing of topical Bactroban (mupirocin) in Aotearoa in the 1990s, with one tube dispensed per 17 people each year, led to the rapid spread of mupirocin resistant Staphylococcus aureus. The prevalence of mupirocin resistant strains went from <1% in 1991 to greater than 20% in 2000.