Table 4. Effect of screening case definitions on estimates of influenza-associated hospitalization annual incidence, Vadu, District Pune, India, May 2009–April 2011.

Screending definition	# of patients meeting screening definition	# (%) patients with specimens positive for influenza virus	Adjusted influenza-associated hospitalization annual incidence per 10,000 persons	% underestimate*
Acute medical hospitalization	3179	665 (20,9%)	44.1	—
ILI**	1632	454 (27.8%)	30.1	32%
ARI***	2183	566 (25.9%)	37.5	15%
FARI†	1659	455 (27.4%)	30.1	32%
SARI‡	87	20 (23.0%)	1.3	97%

^*% underestimate defined as ((1-estimated hospitalization incidence based on use of the given screening definition)/estimated hospitalization incidence based on use of all acute medical hospitalizations as a screening definition) expressed as a percentage).

^**Influenza-like illness (ILI) was defined as fever and either cough or sore throat.

^***Acute respiratory illness (ARI) was defined as >1 of the following: cough, nasal discharge, sore throat, or shortness of breath (based on history).

^†Febrile acute respiratory illness (FARI) was defined as the presence of ARI plus fever.

^‡For persons >5 years, severe acute respiratory illness (SARI) was defined as the presence of ILI and either shortness of breath or difficulty breathing.

For children <5 years, SARI was defined as pneumonia or severe pneumonia as defined by the Integrated Management of Childhood Illness guidelines as any of the following: any general danger sign (i.e. unable to drink or breastfeed, vomiting, convulsions, lethargic, or unconscious), chest indrawing, stridor, or fast breathing on examination.