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Abstract

Introduction: Herein is described a unique case demonstrating the changing epidemiology of Haemophilus influenza in the post-vaccine era. A 36 year old male with history of acute lymphoblastic leukemia status post bone marrow transplant (BMT), in remission and on no immunosuppressive medications, presented the emergency department for evaluation of syncope in the context of several days of fever, productive cough and dyspnea, gradual onset of headache, diffuse back pain and a few loose stools. He was treated presumed community-acquired pneumonia but progressively became more tachypneic, hypotensive and developed altered mental status requiring intubation, central line placement and vasopressors. He was admitted to the ICU under these conditions. The blood cultures were positive for gram negative bacillus and the lumbar puncture was indicative of bacterial meningitis. Bacterial speciation of the cultures confirmed the pathogen was Haemophilus influenza. The patient had successful immunization post-BMT, as confirmed by serology. The final diagnoses for this patient were invasive Haemophilus influenza (serotype A) with meningitis, bacteremia and presumed sinusitis with susceptibility to Haemophilus influenza secondary to previously undiagnosed functional hyposplenism. Haemophilus influenza is a pleomorphic, non-motile, facultative anaerobic gram-negative coccobacillus and a human-specific pathogen. There are encapsulated (typeable) and unencapsulated (nontypeable) strains. Prior to the development of the vaccine, the capsule was thought to be the primary virulence factor, with serotype b being the predominant strain causing clinical disease. Therefore, serotype b is the target of immunizations against Haemophilus influenza. The epidemiology of invasive disease has shifted after wide-spread vaccination, with nontypeable strains causing the majority of invasive infections in all age groups. Despite the common belief that immunizations have eliminated Haemophilus influenza from our differential diagnoses, in the post-vaccine era, the most common presentations of invasive Haemophilus influenza are bacteremia and meningitis. Both encapsulated (non-serotype B) and unencapsulated strains can lead to invasive disease, therefore it is imperative that physicians recognize that, in the case of Haemophilus influenza, immunization does not equal eradication.