Microbiological aspects of bacterial lower respiratory tract illness in children: atypical pathogens

doi:10.1016/j.prrv.2007.07.004

Paediatric Respiratory Reviews

Volume 8, Issue 3, September 2007, Pages 212-220

https://doi.org/10.1016/j.prrv.2007.07.004 Get rights and content

Summary

‘Atypical’ lower respiratory tract pathogens often cause a distinct identifiable syndrome in adults, but in children the clinical presentation of atypical, typical and viral pneumonia is less well differentiated. Specific microbiological investigations are usually required, but an understanding of their strengths and weaknesses is necessary to make interpretation possible. This review examines clinical presentation, microbiology and current evidence surrounding diagnostic techniques for Mycoplasma pneumoniae, Chlamydophila pneumoniae, Chlamydophila psittaci, Bordetella pertussis and Legionella species. Applying an understanding of the investigations to the diagnosis of pneumonia in children may lead to more appropriate patient management by ensuring that they clarify rather than further obscure the diagnosis.

Introduction

The so-called ‘atypical’ pathogens were named for a distinct presentation of clinical disease in adults. In adults, these pathogens are commonly associated with non-respiratory symptoms and bilateral lung disease compared with the classical presentation of pneumococcal lobar pneumonia. This contrasts with the presentation in children which is frequently indistinguishable from that caused by ‘typical’ bacteria and by viruses, as each can cause isolated lobar consolidation and similar systemic responses. This makes identification of the causative organism of lower respiratory tract infection (LRTI) in children even more important and emphasizes the need for appropriate microbiological investigations.

The microbiological diagnosis of respiratory infection with atypical organisms in children is challenging. First, all of the problems applying to typical bacteria remain relevant, including the difficulty of obtaining an appropriate sample. Second, routine culture of these organisms is rarely a viable option. Third, the investigations for each of these pathogens often have limited sensitivity and specificity.

Despite these challenges, the appropriate use of clinical and laboratory information can shed light on the microbiological diagnosis of LRTI in many children. This review examines the current status of diagnostic techniques for Mycoplasma pneumoniae, Chlamydophila pneumoniae, Chlamydophila psittaci, Bordatella pertussis and Legionella species.

Section snippets

Mycoplasma pneumoniae

M. pneumoniae is the smallest known free-living organism. It is implicated in a wide spectrum of clinical disease involving multiple body systems. The most common presentation is with respiratory illness. Although other species of mycoplasma are described, the term mycoplasma here refers only to M. pneumoniae. Although there is no conclusive evidence that specific antibiotic treatment of mycoplasma respiratory infection affects the outcome of disease, it is common to treat symptomatic infection

Chlamydia and Chlamydophila

Chlamydia and the newly differentiated Chlamydophila are obligate intracellular organisms. Three species are prominent human pathogens. Chlamydophila pneumoniae and Chlamydophila psittaci most commonly cause respiratory disease. In the developed world Chlamydia trachomatis is most commonly a urogenital tract pathogen, which also causes neonatal pneumonia and conjunctivitis. In the developing world it is the cause of trachoma.

Immunity after primary infection with Chlamydia species is generally

Chlamydophila pneumoniae

C. pneumoniae is a primary human pathogen without any known animal reservoir. It causes LRTI but is also documented as frequently causing mild or asymptomatic infection. It causes invasive disease by entering cells, reproducing within cytoplasmic inclusions and being released with or without destruction of the host cell. Treatment for diagnosed infection is usually with macrolides or tetracyclines (in children over 8 years);⁹ however, there is no good evidence that this treatment is superior to

Chlamydophila psittaci

C. psittaci is the cause of psittacosis in humans. The natural reservoir for C. psittaci is birds, in which it can be symptomatic or asymptomatic. The bacterium is likely spread by the respiratory route. Humans are generally infected by direct contact with birds or their excreta or indirect contact, such as aerosolization of dead birds with a lawnmower.¹⁴ Person-to-person transmission is rare but can probably occur as psittacosis has been documented in healthcare workers exposed to patients

Legionella

Legionella species are a cause of both pulmonary and extrapulmonary infection. The most common manifestation is acute pneumonia, which may be either community- or hospital-acquired. The genus and the pulmonary infection, Legionnaires’ disease, were named after an outbreak that involved delegates at an American Legion convention in Philadelphia in 1976.¹⁶ Infection with Legionella species may produce significant morbidity and mortality if not recognized and treated promptly.

Legionella are small

Pertussis

Pertussis (whooping cough) is caused by the Gram negative pleomorphic bacterium Bordetella pertussis. Occasionally, similar disease can be caused by B. parapertussis. Although pertussis is part of the routine vaccine schedule in most developed countries, the organism remains a significant cause of disease.

Conclusion

In children, atypical pathogens often cause LRTI indistinguishable from that caused by other organisms. This makes specific microbiological investigation very important in this group. A very large range of novel investigations is available, and the clinician requires an understanding of the relative strengths and weaknesses of these tests for the identification of each pathogen when investigating LRTI. This review provides recommendations to help navigate the quagmire of available tests and to

Educational aims

•
To discuss the characteristics of available tests for atypical lower respiratory tract pathogens as they apply to children.
•
To provide evidence-based recommendations for the use of investigations for atypical pathogens in individual children with pneumonia.

Key points

•
Diagnosis of atypical pathogens is challenging in children.
•
Serological assays rarely provide diagnostic certainty in acute illness.
•
Culture is not generally feasible for atypical pathogens.
•
Nucleic acid amplification tests are likely to be the most useful tests for atypical pathogens.

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Citation Excerpt :
In primary infection IgG antibodies appear much later than IgM antibodies. Secondary and chronic infection often runs without or with low titer of IgM antibodies, while there are frequently high titers of IgA and IgG antibodies [1–3,5,8,27]. In the performed study, positive titer of specific IgA antibodies against Mycoplasma pneumoniae and/or Chlamydophila pneumoniae was observed in 3.5% and 4.9% of the children (respectively), thus suggesting chronic infection.
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Over 2003-2009 period there were 1870 children hospitalized due to pneumonia, of which in 332 (17.8%) the Mycoplasma pneumoniae and/or Chlamydophila pneumoniae etiology was confirmed. Mycoplasma pneumoniae, Chlamydophila pneumoniae, and mixed infection was diagnosed in 198 (10.6%), 102 (5.5%), and 32 (1.7%) children, respectively. The dominant clinical feature in both groups was cough, observed in 186 (93.9%) and 88 (86.3%) children, respectively. Further, reddening of the throat, rhinitis, shortness of breath, fever, enlarged lymph nodes, skin lesions and dyspepsia were also observed. The frequency of specific clinical features in both groups was similar. Statistical relationship (p≤0.05) was observed only in case of skin lesions. In chest x-ray there was no statistical link as for analyzed changes. Interstitial inflammatory changes were most frequently observed.
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CME ReviewMicrobiological aspects of bacterial lower respiratory tract illness in children: atypical pathogens

Summary

Introduction

Section snippets

Mycoplasma pneumoniae

Chlamydia and Chlamydophila

Chlamydophila pneumoniae

Chlamydophila psittaci

Legionella

Pertussis

Conclusion

Educational aims

Key points

CME Section

Clin Microbiol Infect

Chest

J Pediatr

Lancet Infect Dis

Semin Pediatr Infect Dis

Lancet

Mycoplasma pneumoniae and its role as a human pathogen

Clin Microbiol Rev

Mycoplasma pneumoniae infections in Australian children

J Paediatr Child Health

Mycoplasma pneumoniae pneumonia: CT features in 16 patients

Eur Radiol

No evidence of Mycoplasma pneumoniae in acute myringitis

Pediatr Infect Dis J