Influenza H1N1 infection in immunocompromised host: A concise review.

Influenza A (H1N1) infection has a propensity to infect an immunocompromised host (ICH). These patients experience more severe manifestations and related complications with increased mortality. Influenza A (H1N1) infection in ICH differs from non-ICH in terms of clinical features, range of complications, radiological features, treatment response, and outcome. Radiology may show higher number of lesions but with no or minimal corresponding clinical manifestations. Coinfection with streptococci, staphylococci, and Aspergillus further increases mortality. Antiviral resistance compounds the overall picture despite optimal regimen. Use of steroids is detrimental. Extracorporeal membrane oxygenation (ECMO) is usually avoided in ICH. However, ICH groups with influenza A (H1N1) infection complicated by acute respiratory distress syndrome who have received ECMO have recorded mortality up to 61%. Nevertheless, evidence-based recommendation on use of ECMO in ICH is lacking. Annual inactivated influenza vaccine is recommended for most ICH groups with a few exceptions and for their close contacts. Hygiene measures greatly contribute to reducing disease burden. High index of suspicion for influenza A (H1N1) infection in ICH, early antiviral therapy, and treatment of coinfection is recommended. With the threat of transmission of resistant viral strains from ICH to the community, apart from treatment, preventive measures such as vaccination and hygienic practices have a significant role. Through this review, we have attempted to identify clinical and radiological peculiarities in ICH with influenza A (H1N1) infection, treatment guidelines, and prognostic factors. Influenza A (H1N1) infection in ICH may remain clinically silent or mild.