Duration of influenza A virus shedding in hospitalized patients and implications for infection control.
OBJECTIVE
To assess the duration of shedding of influenza A virus detected by polymerase chain reaction (PCR) and cell culture among patients hospitalized with influenza A virus infection.


METHODS
Mayo Clinic (Rochester, Minnesota) hospitals that cater to both the community and referral populations.


METHODS
Patients 18 years old and older who were hospitalized between December 1, 2004, and March 15, 2005, with a laboratory-confirmed (ie, PCR-based) diagnosis of influenza A virus infection were consecutively enrolled. Additional throat swab specimens were collected at 2, 3, 5, and 7 days after the initial specimen (if the patient was still hospitalized). All specimens were tested by PCR and culture (both conventional tube culture and shell vial assay). Information on demographic characteristics, date of symptom onset, comorbidities, immunosuppression, influenza vaccination status, and receipt of antiviral treatment was obtained by interview and medical record review. Patients were excluded if informed consent could not be obtained or if the date of symptom onset could not be ascertained.


RESULTS
Of 149 patients hospitalized with influenza A virus infection, 50 patients were enrolled in the study. Most patients were older (median age, 76 years), and almost all (96%) had underlying chronic medical conditions. Of 41 patients included in the final analysis, influenza A virus was detected in 22 (54%) by PCR and in 12 (29%) by culture methods at or beyond 7 days after symptom onset. All 12 patients identified by culture also had PCR results positive for influenza A virus.


CONCLUSIONS
Hospitalized patients with influenza A virus infection can shed detectable virus beyond the 5- to 7-day period traditionally considered the duration of infectivity. Additional research is needed to assess whether prolonging the duration of patient isolation is warranted to prevent nosocomial outbreaks during the influenza season.
Leekha
Surbhi
S
Department of Internal Medicine, Mayo School of Graduate Medical Education, Mayo Clinical College of Medicine, 200 First Street SW, Rochester, MN 55905, USA.
Zitterkopf
Nicole L
NL
Espy
Mark J
MJ
Smith
Thomas F
TF
Thompson
Rodney L
RL
Sampathkumar
Priya
P
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018929:Cell Culture Techniques; D004279:DNA, Viral / Q000032:analysis; D006760:Hospitalization; D006801:Humans; D017053:Infection Control; D009980:Influenza A virus; D007251:Influenza, Human / Q000635:transmission*; D008875:Middle Aged; D016133:Polymerase Chain Reaction; D011446:Prospective Studies; D013997:Time Factors; D017201:Virus Shedding
D004279:DNA, Viral