Regarding the diagnosis and management of pertussis which ONE of the following is TRUE?
Answer: D: Pertussis is a highly contagious respiratory illness that is transmitted by droplet infection and has approximately an 80% attack rate for susceptible contacts. Humans are the only reservoir and the incubation period is approximately 7–10 days. Morbidity and mortality (0.5–1%) is highest in infants under 6 months of age. Despite vigorous immunization schedules this subset of patients is not protected, as three or more injections are required to confer protection. The current Australian immunization schedule recommends vaccination against pertussis at 2, 4 and 6 months of age, with a booster at 4 years. Furthermore, maternal antibodies do not guarantee protection of the neonate against developing pertussis and it is recommended that women in the last trimester of pregnancy who have been exposed to pertussis should receive chemoprophylaxis.
The laboratory diagnosis of pertussis, irrespective of the technique used, is challenging and unfortunately not a very sensitive tool. While a positive result is useful, a negative result doesn’t exclude pertussis. Commonly used tests for pertussis include culture, PCR, and serology.
Culture of pertussis from nasopharyngeal specimens has traditionally been regarded as the ‘gold standard’ for laboratory diagnosis but, unfortunately, has sensitivity as low as 0–67%. It is important to only collect specimens from the nasopharynx (aspirate rather than a swab) as Bordetella pertussis is found in areas with ciliated epithelium and specimens from the anterior nose, throat and sputum are of little value. PCR is the most sensitive and specific of all investigations and unlike culture specimens can be performed on throat swabs. Furthermore, it is not as readily affected by prior antibiotic therapy and remains positive for longer than cultures. Only IgG and IgA are used in serological testing to make a diagnosis of pertussis. While a raised IgG can occur with both natural infection and vaccination, IgA is only produced after natural infection. For patients presenting early (within the first 3 weeks) and before the start of antibiotic therapy, PCR, immunofluorescence and culture may be useful. For patients who present later, serological testing − which is reliant on an immune response − is often more helpful.
A macrolide antibiotic is the treatment of choice. However, antibiotic therapy will render the patient noninfectious but will be unlikely to alter the course of their illness. The patient will only become noninfectious after 5 days of antibiotic therapy and should therefore be excluded from school/work for this period.
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Regarding assessment of severity of a patient with community-acquired pneumonia (CAP) in the ED, which ONE of the following statements is TRUE?
Answer: B: CAP severity assessment in the ED should be based on the emergency clinician’s clinical judgement based on the history, examination and investigation findings as well as the use of at least one severity scoring system. There are a number of severity scoring systems available, some are more validated than others. The PSI seems to be the most validated but it has a number of disadvantages. Currently, the Australian Therapeutic Guidelines Antibiotic Expert Group recommends the use of SMART-COP score (Table below 1) and CORB score (Table below 2) as severity assessment tools. A significant advantage of using SMART-COP score is its ability to identify the patient who will require intensive respiratory and vasopressor support (IRVS). CORB score may predict the need for IRVS, whereas the PSI is good at predicting the mortality risk but may not identify patients who will clinically deteriorate and require IRVS.
Severity of CAP does not identify the aetiology; neither do the findings on the history, examination and CXR.
SMART-COP SCORE:
CORB SCORE:
Patients with 2 or more points is considered as having severe CAP and a high risk of needing IRVS.
Regarding use of blood culture and sensitivity in a patient with community-acquired pneumonia (CAP), which ONE of the following statements is TRUE?
Answer: D: The evidence suggests that routine use of blood cultures to diagnose the aetiological agent in a patient who is likely to have CAP is of low value. In admitted patients only up to 16% of the blood cultures become positive. However, when positive this can confirm the aetiological agent of CAP. As a result, blood cultures are recommended in the following selected subgroups of patients with CAP including:
There is a moderate level of evidence to support blood cultures in the above subgroups. When empiric antibiotic treatment is initiated in the ED for CAP according to the locally accepted therapeutic guidelines, the subsequent results of the blood culture rarely result in a change of the initial antibiotic therapy.
Regarding the aetiological diagnosis of community-acquired pneumonia (CAP), which ONE of the following statements is FALSE?
Answer: A: It is difficult to predict the causative organism associated with pneumonia with the CXR findings as the changes are often non-specific. However, some radiological changes are more likely to be associated with a specific group of organisms. These include:
Sputum culture results are not likely to change the antibiotic treatment. However, when correctly collected (i.e. prior to initiation of antibiotic therapy) and when the specimen is not heavily contaminated with squamous epithelial cells, the chance of identifying a causative organism increases up to 40%. The results of the sputum specimens collected after the commencement of antibiotics can be misleading. Similarly, the yield from blood cultures is relatively low. In general, blood culture may yield a 5–10% positive result in admitted patients with CAP. In Streptococcus pneumonia the blood culture yield is said to be 15–30%. The yield of blood cultures increases with increasing severity of pneumonia.
In patients with suspected Streptococcus pneumonia, Streptococcal urinary antigen assay can be performed on routinely collected urine and this can be done even after the commencement of antibiotics. Similarly Legionella pneumophila serotype 1 can be identified with Legionella urinary antigen assay. This test is indicated in patients requiring intensive care admission, alcoholics and in a recently returned traveller.
Testing for nucleic acid with polymerase chain reaction (PCR) in nose and throat swabs is usually helpful to identify a respiratory viral and influenza aetiology of pneumonia. For identification of atypical organisms often antibody testing on a set of acute and convalescent sera is used.
Regarding pneumonia caused by Staphylococcus aureus, all of the following statements are correct EXCEPT:
Answer: B: Pneumonia caused by S. aureus may originate both as a community-acquired and hospital-acquired infection. It may account for up to 25% of pneumonia occurring in nursing home residents. It is also more common in intravenous drug users. During influenza epidemics, S. aureus pneumonia may occur as a secondary infection in otherwise healthy adults. Radiological findings on the CXR vary and empyema and cavity formation may be present, but these finding are not common. A S. aureus infection tends to cause comparatively severe pneumonia and hence associated with higher incidence of septic shock and mortality.
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