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Laboratory diagnosis of paediatric lower respiratory tract infection.



The burden of respiratory tract infections (RTIs) in children is extremely high in industrialised and developing countries, with nearly 50% of paediatric consultations in industrialised countries related to RTIs. (1)

Viruses have been shown to cause up to 90% of pneumonias, especially in the first year of life, with the respiratory syncytial virus respiratory syncytial virus (sĭnsĭsh`əl): see cold, common.  the most important pathogen. This percentage decreases to approximately 50% by school-going age. Viral pneumonias are frequently complicated by bacterial infections, and mixed infections are common. Streptococcus pneumoniae is common in all age groups, and complications are usually associated with pneumococcal pneumococcal /pneu·mo·coc·cal/ (-kok´al) pertaining to or caused by pneumococci.  infections or co-infections.

The majority of patients with viral lower respiratory tract infections (LRTIs) are admitted to hospital because of bronchiolitis Bronchiolitis Definition

Bronchiolitis is an acute viral infection of the small air passages of the lungs called the bronchioles.
Description

Bronchiolitis is extremely common.
 and pneumonia.

Laboratory diagnosis

Laboratory confirmation of the diagnosis is difficult and colonising flora may hamper the detection of true pathogens.

Although respiratory virus infections cause significant morbidity and mortality, laboratory diagnosis may not be needed in all patients or under all conditions. The indications for laboratory diagnosis of viral LRTIs are not clearly defined. However, infections that lead to hospital admission or prolong hospital stay, such as moderate to severe LRTI LRTI Lower respiratory tract infection  or fever syndrome, especially in young infants or immunocompromised children, warrant laboratory investigation. Other possible indications include an effort to stop unnecessary prescription of antimicrobials, to decrease further unnecessary diagnostic testing, to direct antiviral therapy or to define seasonal or epidemic disease in a specific community. (2)

In the past tissue culture techniques, which were the gold standard, were used to detect respiratory viruses. However, these techniques are time consuming, with decreased sensitivity, compared with molecular testing that is only performed in a few specialised laboratories. Serology is rarely helpful during acute disease owing to the possible time delay before seroconversion. Several antigen-based rapid diagnostic assays are available, including immunofluorescence and ELISA ELISA (e-li´sah) Enzyme-Linked Immuno-Sorbent Assay; any enzyme immunoassay using an enzyme-labeled immunoreactant and an immunosorbent.

ELISA
n.
 assays, but nucleic acid amplification tests such as the multiplex polymerase chain reaction polymerase chain reaction (pŏl`ĭmərās') (PCR), laboratory process in which a particular DNA segment from a mixture of DNA chains is rapidly replicated, producing a large, readily analyzed sample of a piece of DNA; the process is  (PCR) offer a broad range of diagnostic capabilities where multiple aetiologies can be detected. These can include the detection of influenza virus A, B and C, adenovirus, metapneumovirus, RSV A and B, rhinovirus rhinovirus

Any of a group of picornaviruses capable of causing common colds in humans. The virus is thought to be transmitted to the upper respiratory tract by airborne droplets.
 A, parainfluenza virus 1, 2 and 3, echovirus echovirus /echo·vi·rus/ (ek´o-vi?rus) an enterovirus isolated from humans, separable into many serotypes, certain of which are associated with human disease, especially aseptic meningitis. , bocavirus and coronavirus in a single test.

A range of samples, such as nasopharyngeal aspirates or swabs and bronchoalveolar lavage specimens, are appropriate for PCR processing. Nasopharyngeal swabs present an easy method of obtaining a specimen if other respiratory samples are difficult to obtain. Samples should preferably not be frozen or stored for more than 72 hours before processing.

Confirmation of bacterial aetiology can be performed by conventional culture of the organism or by antigen detection from a urine sample, e.g. in the case of Legionella Legionella /Le·gion·el·la/ (le?jah-nel´ah) a genus of gram-negative, aerobic, rod-shaped bacteria (family Legionellaceae), normal inhabitants of lakes, streams, and moist soil; they have often been isolated from cooling-tower water,  or S. pneumoniae. Several PCR assays are available for the detection of typical and atypical bacterial agents.

An adequate, expectorated sputum specimen should contain many neutrophils and few or no squamous epithelial cells Squamous epithelial cells
Thin, flat cells found in layers or sheets covering surfaces such as skin and the linings of blood vessels and esophagus.

Mentioned in: Heartburn
. The latter are indicative of contamination with saliva. If possible, patients should brush their teeth and/or rinse their mouths well with water before attempting to collect the specimen in order to reduce the possibility of contaminating it with food particles or oropharyngeal oropharyngeal /oro·pha·ryn·ge·al/ (-fah-rin´je-al)
1. pertaining to the mouth and pharynx.

2. pertaining to the oropharynx.
 secretions. An induced sputum sample should be considered if expectorated sputum cannot be obtained.

In bronchoscopy Bronchoscopy Definition

Bronchoscopy is a procedure in which a cylindrical fiberoptic scope is inserted into the airways. This scope contains a viewing device that allows the visual examination of the lower airways.
 and aspirated specimens reduction of contamination may be accomplished by a head-down position to reduce gravitational flow of saliva. Oral contamination may successfully be reduced by using a telescoping double catheter with a plug to protect the brush or by a sheathed brush. The use of the telescoping plugged catheter and bronchoalveolar lavage increases the overall diagnostic yield.

A processing delay of more than a few hours may result in loss of recovery of fastidious pathogens and overgrowth of oropharyngeal flora.

References

(1.) Schaad UB. Prevention of paediatric respiratory tract infections: emphasis on the role of OM-85. Eur Respir Rev 2005; 14: 7477.

(2.) Henrickson KJ. Advances in the laboratory diagnosis of viral respiratory disease. Pediatr Infect Dis J 2004; 23(1S): S6-S10.

MARTHINUS SENEKAL, MB ChB, MMed (Micro Path)

Clinical Microbiologist, Pathcare Reference Laboratory, Goodwood
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Title Annotation:More about ... Microbiology
Author:Senekal, Marthinus
Publication:CME: Your SA Journal of CPD
Geographic Code:6SOUT
Date:Nov 1, 2008
Words:668
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