Pathology
H1N1 | H5N1 | References | Blogs
The primary organs damaged in H1N1 infections are the lungs. Damage may either be due to directly to the virus or as a result of a secondary bacterial infection, viral and bacterial pneumonia, respectively. The role of direct action of the new H1N1 virus versus bacterial superinfections in severe cases is still unsettled. Early studies indicated few or no bacterial infections in lab-confirmed cases. However, a more recent study (Louie et al. 2009) demonstrated bacterial infections of the lungs in 29% of the patients. Bacteria included Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Streptococcus mitis and Haemophilus influenzae, in decreasing order of frequency.
The Figure above consists of two slides showing Streptococcus pneumoniae infection in a patient with confirmed pandemic H1N1 virus infection. [From Louie et al. 2009]
According to a recent email sent by the Regional Liaison Officer, Region IV, H1N1 Response Surveillance and
Epidemiology Team, Centers for Disease Control and Prevention, the CDC is currently looking for clusters of Hemorrhagic Pneumonia:
The CDC says that there have been some anecdotal reports of possible “hemorrhagic pneumonia” cases among influenza patients who have died or been hospitalized for severe illness. The phrase “hemorrhagic pneumonia” is somewhat outdated, and most clinicians will not use the term to describe this condition, which can be a very rare complication of viral respiratory infection. Some other terms that can be used to describe this include diffuse alveolar hemorrhage (DAH), which can be caused by infections but doesn’t have to be, and hemorrhagic pneumonitis. In any event, it’s a serious complication that will sometimes lead to acute respiratory distress syndrome (ARDS). It occurs very rarely as a complication of seasonal influenza, and there is some concern that it might be more common in H1N1 infections.
The CDC is asking state health officials to look out for possible cases that may involve clusters of patients who might have these symptoms, or a large proportion of cases with these symptoms (e.g., 4 of 5 deaths). They will invariably be among the most severely ill influenza patients (i.e., deaths, ICU patients).
This is a hard diagnosis to make, and the most telling symptom may be hemoptysis (bloody sputum, frothy bloody cough), although not all cases will have it.
- Acute onset of rather more severe respiratory infection (dyspnea–difficulty breathing–is common)
- Hemoptysis is often seen on initial presentation (~70% of cases)
- CXR and physical exam will suggest alveolar infiltrates (radiographic opacities)
- Diagnosis is usually made by BAL (brochoalveolar lavage) and pathology testing (increasingly more hemorrhagic fluid/secretions from sequential BAL
Email sent by Regional Liaison Officer, Region IV, H1N1 Response Surveillance and Epidemiology Team, Centers for Disease Control and Prevention
Questions concerning possible cases or this email may be directed to Medical Epidemiologist Zach Moore, MD, at the North Carolina Division of Public health at zach.moore@dhhs.nc.gov.
The primary organs damaged in H5N1 infections are the lungs. Patients often require ventiliation and die of acute respiratory distress syndrome (ARDS). Damage to the lungs is due to H5N1 infection itself and not to secondary bacterial infection. Cytokine dysregulation is thought to be involved.
H5N1 is also able to cause systemic infection and damage multiple organs including the brain.
Mauad et al. (2009) Lung Pathology in Fatal Novel Human Influenza A (H1N1) Infection. Am J Respir Crit Care Med.
Louie et al. (2009) Hospitalized Patients with Novel Influenza A (H1N1) Virus Infection --- California, April--May, 2009. MMWR Weekly. May 22, 2009. 58: 536-541.
Napolitano et al. (2009) Intensive-Care Patients With Severe Novel Influenza A (H1N1) Virus Infection --- Michigan, June 2009. MMWR Weekly. May 22, 2009. 58: 749-752.
Louie et al. (2009) Bacterial Coinfections in Lung Tissue Specimens from Fatal Cases of 2009 Pandemic Influenza A (H1N1) --- United States, May--August 2009. MMWR Weekly. October 2, 2009. 58: 1071-1074.
Update on Avian Influenza A (H5N1) Virus Infection in Humans
Writing Committee of the Second World Health Organization Consultation on Clinical Aspects of Human Infection with Avian Influenza A (H5N1) Virus. New Eng. J Med. (2008) 358:261-273
Gu et al. (2007) H5N1 infection of the respiratory tract and beyond: a molecular pathology study. Lancet. 370:1137-1145.
van Riel et al. (2007) Human and Avian Influenza Viruses Target Different Cells in the Lower Respiratory Tract of Humans and Other Mammals. Am J Pathol. 171: 1215–1223.
Chutinimitkul et al. (2006) H5N1 influenza A virus and infected human plasma . Emerg Infect Dis.
Ferreting out the dangers of swine flu: A discussion of two animal model studies of the new H1N1 flu virus.
July 6, 2009
More evidence that the new H1N1 virus is more dangerous than seasonal flu: The new Kawaoka paper.
July 13, 2009
It hurts
July 30, 2009
Severe Strains of H1N1?
August 29, 2009
An analysis of the ferret co-infection paper
September 1, 2009
New strain of H1N1 that kills rapidly?
September 18, 2009
Coughing up blood
September 26, 2009
Lethal mutation observed in American cases?
September 27, 2009
Another report of more virulent pandemic virus in India
October 29, 2009
How does pandemic H1N1 kill?
November 9, 2009