Influenza burden of illness: estimates from a national prospective survey of household contacts in France.
BACKGROUND
The burden of influenza among ambulatory patients is still relatively unknown, although this knowledge is crucial for evaluating strategies against influenza. We estimated the impact of influenza in terms of uncomplicated morbidity and its consequences on health care utilization and lost workdays.


METHODS
A national prospective household contact study between January 4, 2000, and March 15, 2000, in France recruited the households of 946 persons who visited a physician (index cases); 395 households with influenza-positive index cases completed the follow-up, which assessed the clinical impact of influenza, medical visits, treatment, and lost workdays in these index cases and their contacts.


RESULTS
Of 817 assessable household contacts, 313 developed clinical influenza (secondary cases); 178 (57%) of them visited a physician at least once (consulting secondary cases). The median duration of illness was 8 days (95% confidence interval [CI], 7-8 days) in index cases, 7 days (95% CI, 7-8 days) in consulting secondary cases, and 4 days (95% CI, 3-5 days) in nonconsulting secondary cases (P<.001); the median duration of treatment in these groups was 8 days (95% CI, 8-9 days), 8 days (95% CI, 7-10 days), and 5 days (95% CI, 4-6 days), respectively (P<.001); and their mean +/- SD number of lost workdays was 4.0 +/- 2.8, 2.9 +/- 2.5, and 0.3 +/- 0.6, respectively, in working adults (P<.001).


CONCLUSIONS
These results confirm the substantial burden of illness of influenza. The results should be useful for evaluating the cost-effectiveness of strategies against influenza.
INSERM U444, Faculté de Médecine Saint-Antoine, 27 rue Chaligny, 75571 Paris CEDEX 12, France. carrat@u444.jussieu.fr
Fabrice
F
Carrat
Camille
C
Sahler
Sylvie
S
Rogez
Marianne
M
Leruez-Ville
François
F
Freymuth
Catherine
C
Le Gales
Martine
M
Bungener
Bruno
B
Housset
Marlène
M
Nicolas
Christine
C
Rouzioux
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000911:Antibodies, Monoclonal; D002648:Child; D002675:Child, Preschool; D017281:Cost of Illness; D005191:Family Characteristics; D005260:Female; D005602:France / Q000453:epidemiology; D006296:Health Services / Q000706:statistics & numerical data; D006306:Health Surveys; D006801:Humans; D007223:Infant; D009980:Influenza A virus / Q000302:isolation & purification; D009981:Influenza B virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000175:diagnosis* / Q000191:economics* / Q000453:epidemiology / Q000821:virology; D008297:Male; D008875:Middle Aged; D009297:Nasal Mucosa / Q000821:virology; D016133:Polymerase Chain Reaction; D011446:Prospective Studies; D011788:Quality of Life; D018582:Sick Leave; D011795:Surveys and Questionnaires; D013997:Time Factors
D000911:Antibodies, Monoclonal