Fatal cases of 2009 H1N1 influenza can damage cells throughout the respiratory airway, much like damage caused by the viruses behind the 1918 and 1957 flu pandemics, according to a new study in the Archives of Pathology & Laboratory Medicine. Researchers examining 34 New York autopsies found damage primarily in the upper airways—including the trachea and bronchial tubes—but also in the lower airway, even deep in the lungs. Secondary bacterial infection was present in more than half the victims.

 

The study's findings gives clinicians a better picture of the disease, assistance that should help inform patient management, says Anthony Fauci, director of National Institute of Allergy and Infectious Diseases. That help comes at a crucial point in the national vaccination drive, which is ramping up with more plentiful supplies even as interest in getting vaccinated wanes among many young at-risk adults.

 

“In all cases, the uppermost regions of the respiratory tract—the trachea and bronchial tubes—were inflamed, with severe damage in some cases. In 18 cases, evidence of damage lower down in the finer branches of the bronchial tubes, or bronchioles, was noted. In 25 cases, the researchers found damage to the small globular air sacs, or alveoli, of the lungs,” says Jeffery Taubenberger, at NIAID.

 

Young people still remain in more peril than the elderly the report says. While most deaths from seasonal influenza occur in adults over 65 years old, more than half of the 34 New York City deaths studied in the report were among those 25 to 49 years old. Two infants were also among the fatal cases.

 

But additional risk lies in underlying medical conditions. Of those autopsied for the study, 91 percent suffered conditions such as heart disease or respiratory disease, including asthma, before catching 2009 H1N1 influenza. Some 72 percent of the adults and adolescents who died were obese, a finding in line with earlier reports linking obesity with an increased risk of death from the H1N1 flu.

 

The researchers also found 55 percent of those autopsied were positive for secondary infections. That raises the possibility, say the authors, that community-acquired bacterial pneumonia is playing a role in the current pandemic. “Even in an era of widespread and early antibiotic use,” write the authors, “bacterial pneumonia remains an important factor for severe or fatal influenza.”