Influenza

OVERVIEW

• caused by influenza A and B viruses

CLINICAL FEATURES

• fever (>38 C)
  +/- one systemic symptoms (myalgia)
  +/- one respiratory symptoms
  -> 70% chance of having influenza

INVESTIGATIONS

• nasopharyneal viral swab

MANAGEMENT

Active Treatment

• neuraminidase inhibitors are of no benefit unless started within 48 hrs of patient developing symptoms
• even if started within 48 hours -> will only shorten duration of illness by 1 day
• does reduce incidence of complications
• resistance has emerged
• oseltamivir 75mg Q12 hrly for 5/7 or until swab negative (2mg/kg)
• zanamivir 10mg INH Q12 hrly for 5/7

Prophylaxis

• current influenza vaccine prior to winter
• vaccination for at risk groups – health care workers, > 65 years, Aboriginal/Maori/PI > 50 years, specific chronic diseases
• can use neuraminidase inhibitors after exposure

SWINE-ORIGIN INFLUENZA VIRUS

• SOIV = H1N1 = sub-type of influenza A -> caused the pandemic of 2009
• caused 17,000 deaths by the start of 2010
• infection caused any of the influenza viruses endemic in pigs

Particular important characteristics:

• complete dominance over the seasonal influenza viruses
• severely effected = pregnant, children < 2, respiratory condition, immunosuppression, obesity
• case fatality rate of 1.3%
• respiratory conditions = obesity, asthma, COPD
• immunocompromised = solid organ transplant, bone marrow transplant, cancer

Pulmonary Complications

• death (typically aged 15-60 yrs)
• pneumonia
• superinfection (MRSA, Streptococcus pneumoniae, S. aureus, streptococcus pyogenes, H. influenzae, Streptococcus mitis, atypical pneumonia, Aspergillus)
• VAP (Pseudomonas aeruginosa, Acinetobacter baumannii, MRSA, E. coli)
• ARDS
• PE

Extra-pulmonary Complications

• pericarditis
• myocarditis
• renal failure
• elevated CK -> rhabdomyolysis
• encephalitis/cerebritis -> seizures