RESPIRATORY TRACT INFECTIONS
Culture of sputum is only indicated in the investigation and management of lower respiratory tract infection/pneumonia (NOT of non-specific cough or bronchitis) and if there is no response to first line agents1. Culture of sputum is of limited value because:
the investigation is insensitive, as a good representative sample is difficult to obtain.
culture results can be misleading as the sample becomes contaminated with upper respiratory tract flora during expectoration.
Early morning specimens are likely to be of better quality and less contaminated than random specimens. A deep cough specimen should be collected before brushing teeth or inserting dentures and after rinsing the mouth with tap water. Deliver for culture as soon as possible.
For "persistent cough" without chest signs consider serology for atypical agents, and if indicated culture for mycobacteria.
Recent BTS Guidelines (2001/2004) detail the aetiology, investigations and management.
S. pneumoniaeis the most frequently identified pathogen. The prevalence of penicillin resistant pneumococci is still low in this area and does not impact on first line antibiotic treatment unless there is a history of recent travel abroad.
Atypical pneumonia has a less acute onset with predominant constitutional symptoms, headache, and upper respiratory tract symptoms. However it is often indistinguishable from bacterial pneumonia. Causative agents are:Mycoplasma pneumoniae, Legionella sp., Chlamydia sp. (C. psittaci, C. pneumoniae) and viruses. These infections are often mild and sub-clinical and self-limited but cough may be persistent. Lack of response to amoxycillin is suggestive of atypical pathogens.
Sputum culture not recommended routinely in mild pneumonia. Consider sputum examination for patients who do not respond to empirical first-line antibiotics.
Patients with severe pneumonia require hospitalization. A single dose of antibiotic is recommended in severe pneumonia if there is likely to be a delay of over two hours prior hospital admission e.g. parenteral penicillin G or amoxycillin 1 g orally or erythromycin.
CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD)
Although the precise role of bacterial pathogens in the pathogenesis of COPD is as yet unclear, it is acknowledged that bacterial infection contributes to acute exacerbations in approximately 50% of patients.
Up to 80% of patients with COPD are colonised withStrep. pneumoniae, H. influenzae, Moraxella catarrhalis and other upper respiratory tract pathogens. Routine culture of sputum is therefore unwarranted. Send sputum cultures from non-responders only.
Clinical studies show no benefit from antibiotic treatment over placebo except in the most severely affected patients. Prescribe an antibiotic if two of more of the following are present during an exacerbation: increased breathlessness, increased sputum volume, development of purulent sputum.
The decision to treat and the choice of antibiotic may be influenced by the duration and severity of symptoms, the frequency of infections, previous response to antibiotic therapy and the presence of cardio-pulmonary comorbidity.
Useful antibiotics include amoxicillin, erythromycin and doxycycline.
In longstanding bronchitis, (usually associated with thickened scarred bronchi) ciprofloxacin 500 mg bd may be useful because of its excellent tissue penetration and its wider spectrum which includes most Gram negative pathogens. It should not be used as a first line agent as it does not cover pneumococci reliably.
Influenza and pneumococcal vaccines are recommended.
CYSTIC FIBROSIS AND BRONCHIECTASIS
These patients need a carefully tailored programme of antibiotic treatment. Based on sputum culture and clinical progress.
Acute bronchitis is usually associated with a generalised respiratory tract infection caused be a range of viruses - the common cold viruses and the more invasive adeno and influenza virus. Secondary infection with bacterial agents is probably rare but should be considered in the elderly and patients with cardiopulmonary diseases. Treat empirically.
The "atypical" agentsMycoplasma pneumoniae and Chlamydia pneumoniae are relatively common non viral causes of upper respiratory tract infection and bronchitis. Infections tend to be insidious in onset and may result in severe and prolonged cough usually indistinguishable from viral infection but may be more recognisable during outbreaks
(M. pneumoniae every four years). Pneumonia is a complication in a small proportion of patients.
Culture not indicated unless there is evidence of pneumonia. Purulent discharge does not always indicate bacterial infection. Send serum for serology for atypical respiratory pathogens ten or more days after onset if indicated.
Antibiotic therapy is not indicated for uncomplicated acute bronchitis i.e. when there is no evidence of pneumonia. The threshold for active intervention should be lowered in the elderly and the in the presence of co morbid conditions. Treat empiricaloly. Although morbidity may be prolonged, these infections are self limited so uncomplicated infections do not warrant antibiotic treatment. Also see atypical pneumonia.
or erythromycin or tetracycline which should also cover atypical agents
WHOOPING COUGH (Bordetella pertussis)
Adults with previous immunity may not present with the typical cough accompanied by vomiting. Infection should be suspected during an outbreak or following contact. Antibiotic treatment is mandatory.
Laboratory confirmation is mandatory if infection is suspected. Take a nasopharyngeal specimen for culture using a swab with a fine wire shaft (pernasal swab). The swab should be passed horizontally backwards via the anterior nares and should be withdrawn as soon as it touches the nasopharynx when an involuntary cough will be elicited. (External marking – external auditory meatus). Alternatively send a specimen for pertussis antibodies (cough over 3 weeks in adults or 2 weeks in children).
erythromycin 500 mg 6 hrly, 14 days
Household contacts of confirmed or suspected cases of pertussis may require prophylaxis. Contact Public Health for advice.
erythromycin 500 mg 6 hrly, 7 days
This is unlikely to be due to persistent pneumonia so sputum for bacterial culture is not
indicated. Consider the following:
Sinusitis with post-nasal drip
Atypical respiratory pathogens
1. British Thoracic Society: Standards of Care Committee. Guidelines
for the Management of
Chronic Obstructive Pulmonary Disease. Thorax 1997;52(Suppl 5):S1-S27.
2. British Thoracic Society Guidelines for the Management of Community
Pneumonia in Adults. Thorax 2001;56(Suppl 4):1-64. Update on BTS website 2004.