Pediatric Haemophilus Influenzae Infection Workup

Updated: Apr 04, 2016
  • Author: Mobeen H Rathore, MD, CPE, FAAP, FIDSA; Chief Editor: Russell W Steele, MD  more...
  • Print

Laboratory Studies

See the list below:

  • Culture

    • This is the most important laboratory study in the context of suspected Haemophilus influenzae disease.

    • In children, the organism causing these infections is blood borne: hence, blood culturing is important in all cases.

    • H influenzae can be cultured from samples of CSF, synovial fluid, pleural and pericardial fluid, and leading-edge aspirates of cellulitis.

  • Antigen detection

    • Numerous methods are available for identifying the H influenzae type b (Hib) PRP capsular polysaccharide antigen in clinical specimens.

    • Suitable specimens for study may be obtained from urine and CSF. These are particularly helpful in the patient who has been pretreated with antimicrobial therapy.

    • Antigen detection has little use in clinical practice, except in the situation mentioned above; most clinical laboratories do not offer this test.

  • Biochemical identification

    • Biochemical identification of H influenzae is based on the demonstration that growth in rich media (blood agar) is dependent on supplements, namely, factors X and V. Factor X is a heat-stable iron-containing protoporphyrin (hemin) that is essential for the function of enzymes in the electron-transport chain in aerobic metabolism. Factor V is the heat-labile coenzyme nicotinamide adenine dinucleotide (NAD).

    • Although both factors are present in erythrocytes, factor V must be released from the cell to sustain its growth; hence, standard blood agar is an unsatisfactory media for the growth of H influenzae. The lysis of RBC releases factor V, providing an exogenous source such as that in chocolate agar.

    • The metabolic requirement of factors X and V for growth remains the major basis for the laboratory identification of H influenzae. The growth requirements of H influenzae are fastidious, and the organism rapidly loses viability; therefore, clinical specimens must be handled expeditiously.

    • After overnight incubation, gray colonies appear; these have a diameter of 0.5-0.8 mm and are rough or granular. Encapsulated strains typically produce larger mucoid or glistening colonies.


Imaging Studies

See the list below:

  • Chest or lateral neck radiography, brain CT echocardiography, and technetium bone scanning may be appropriate.

  • Imaging studies depend on the clinical syndrome.

    • In epiglottis, lateral neck radiography can be helpful if the clinical presentation is subtle, but the study should be performed cautiously, without undue delays, and a physician experienced in airway management should be present.

    • Approximately 50% of patients with pneumonia have evidence of pleural involvement at initial radiographic examination. Pneumonia can have a segmental, subsegmental, interstitial, or lobar pattern.



See the list below:

  • Procedures depend on the clinical circumstances. Necessary procedures may include the following:

    • Lumbar puncture

    • Arthrocentesis

    • Pericardiocentesis

    • Endotracheal intubation or tracheostomy

    • Subdural tap

    • Leading-edge aspirate


Histologic Findings

See the list below:

  • H influenzae is a small gram-negative coccobacillus that may have considerable microscopic pleomorphism, which necessitates the careful and cautious interpretation of Gram stains of clinical specimens .