Wiler, Jennifer L. MD, MBA
A 41-year-old man presents with 10 days of cough, fever, myalgia, congestion, diarrhea, and shortness of breath. He has no previous medical problems.
He is found to be hypoxic and in shock. His chest x-ray is shown. What diagnoses are you concerned about?
Continued on p. 24.
Diagnosis: Post-Influenza Pneumonia
Influenza is one of the most common seasonal communicable diseases, and has resulted in endemics resulting in millions of deaths worldwide. Bacterial co-infection complications were reported to be 18-34 percent during the 2009 H1N1 pandemic, and as high as 55 percent based on autopsies of influenza victims. (JAMA 2013;309:275.) Bacterial co-infection is rare (0.5% cases) in healthy young adults and up to three percent in patients with known risk factors for post-influenza complications. (Int J Infect Dis 2012;16:e321.)
The influenza virus is transmitted primarily via respiratory droplets, and it requires close contact between the source and recipient (approximately one meter). These relatively large particles can be transmitted by contact with a contaminated surface or by propulsion into the air (by a sneeze from a vector). Smaller partial vaporization transmission, however, is also thought to be a possible mechanism. Epidemics tend to occur in the fall and winter, but can take place as late as May.
The incubation period for influenza is two days on average, but can range from one to four days. Viral shedding occurs one day prior to symptom onset, and can last as long as 10 days in immunocompetent adults and children. Immunocompromised persons can shed three to five times longer.
Colonization of the nasopharynx (e.g., Streptococcus pneumoniae and Staphylococcus aureus) has been identified as a risk factor for developing bacterial co-infection and increases the risk of ICU admission and death. (PLoS One 2009;4:e8540; J Infect Dis 2008;197:1226; Crit Care Med 2012;40:1487.)
The symptoms of the flu include acute onset of dry cough, sore throat, congestion, fever, malaise, myalgia, headache, and in children, nausea, vomiting, and otitis. Symptoms tend to resolve within one week, but can cause viral pneumonia and predispose patients to develop secondary bacterial infections including pneumonia, otitis, and sinusitis, and less commonly pericarditis, myocarditis, encephalopathy, and transverse myositis.
Patients who are immunocompromised, obese, at the extremities of age, pregnant, or have underlying cardiopulmonary, renal, hepatic, neurologic, and metabolic disease are at increased risk for developing complications from influenza and death. (MMWR Recomm Rep 2010;59[RR-8]:1.)
Laboratory validation of influenza is recommended in those patients who are high risk, in situations where there could be an outbreak, where management decisions will be affected by the result, and in patients with suspected influenza who are being hospitalized. A variety of different tests are on the market, including viral culture, serology, rapid antigen testing, polymerase chain reaction (PCR), and immunofluorescence assays. Most require collection of nasopharyngeal fluid, ideally within the first four days of the infection. Rapid tests are as high as 70% sensitive and 90% specific, and can give results within 15 minutes. Some detect only type A or only A/B, but some distinguish between A and B. (MMWR 2012;61:873.)
Two FDA-approved influenza antiviral medications are recommended for use in the United States during the 2012-2013 influenza season: oseltamivir (Tamiflu) and zanamivir (Relenza). (See FastLinks.) The CDC recommends antiviral medication initiation as rapidly as is possible (ideally within 48 hours of symptoms onset), but studies show a benefit of antiviral medication for patients with confirmed or suspected influenza who have severe or rapidly progressive illness, are hospitalized, or who are at high risk for complications (under age 2 or over 65, immunosuppressed, pregnant or within two weeks postpartum, younger than 19 who are taking long-term aspirin therapy, American Indians or Alaska Natives, morbidly obese, residents of nursing homes or long-term care facilities, or who have a history of chronic pulmonary, cardiovascular, renal, hepatic, hematologic, metabolic, neurologic, or neurodevelopment conditions). (JAMA 2009;301:1034; Clin Infect Dis 2011;52:457.)
Chemoprophylaxis with oseltamivir and zanamivir is recommended to control outbreaks among high-risk persons in institutional settings, but is generally not recommended for widespread use. Vaccination is the primary prevention strategy recommended by infectious disease specialists and the CDC. This year's vaccination appears to be 60 percent effective in preventing influenza, but has been shown to decrease flu-related illness, antibiotic use, work absence, hospitalization, and death. (MMWR 2013;62:32.) The CDC currently recommends vaccination even mid-flu season.
Patients with confirmed or suspected bacterial co-infection should be treated aggressively and early with antibiotics. Patients with severe or necrotizing pneumonia or sepsis should be empirically treated for MRSA. (JAMA 2013;309:275.)
This patient was diagnosed with Influenza A and septic shock. He had a prolonged hospitalization during which he developed severe ARDS and respiratory failure, renal failure, and critical neuropathy and myopathy. He was found to have Streptococcus pneumonia bacteremia from a confirmed pulmonary source. He survived to transfer to a long-term care facility on supplemental oxygen through a tracheostomy.
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* Read the CDC's summary of influenza antiviral medications at http://1.usa.gov/WrPAVV.)
* “Prevention and Control of Influenza with Vaccines” from the CDC is available at http://1.usa.gov/Xbswyn.
* View the CDC report, “Early Estimates of Seasonal Influenza Vaccine Effectiveness,” at http://1.usa.gov/YFDSKR.
* Read all of Dr. Wiler's past columns at http://bit.ly/WilerConsult.
* Comments about this article? Write to EMN at firstname.lastname@example.org.
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