CHICAGO - Walgreen Co said February sales at stores open at least a year rose just 0.4 percent, crimped by a lower incidence of the flu versus a year earlier.

The rise was nearly in line with the 0.5 percent increase analysts had anticipated, according to Thomson Reuters data. Walgreen's shares rose 1.7 percent to $35.87 on Wednesday morning.

It was the first monthly same-store sales rise at Walgreen, the largest U.S. drugstore chain, since November.

Prescription and general merchandise sales were both pressured by the mild winter flu season, Walgreen said. Also, consumers continued to hold off buying discretionary items.

All drugstores were expected to feel the pressure of a mild winter flu season following the busy autumn. The percentage of U.S. patients visiting doctors for influenza-like illness was just 1.8 percent in the week that ended February 20, down from 7.7 percent at the end of October, according to the Centers for Disease Control and Prevention.

Same-store sales at Walgreens' pharmacy counters rose 0.9 percent, topping analysts' expectations for a 0.6 percent gain. Generic drug introductions cut 2.4 percentage points from comparable pharmacy sales, the company said.

While generic medications sell for less than their branded counterparts, they are typically more profitable for drugstores to sell. Brand-name drugs that faced new generic competition over the past year include Johnson & Johnson's Risperdal schizophrenia drug.

The number of prescriptions filled at stores open at least a year rose 3.6 percent, aided by more patients filling 90-day prescriptions, which count as three in the month that they are sold. Prescription sales also got a slight boost from pharmacists who can now administer H1N1 flu vaccinations.

General merchandise same-store sales fell 0.6 percent, while analysts had expected a 0.9 percent decline.

Total sales climbed 3.2 percent to $5.31 billion.

Walgreen had 7,179 drugstores at the end of February, 501 more than a year earlier. That tally includes 59 stores acquired over the last year. It does not include the pending acquisition of New York's Duane Reade.

Analysts expect Rite Aid Corp , the third-largest U.S. drugstore chain, to post a 1.7 percent decline in February same-store sales on Thursday. That would mark its ninth consecutive monthly drop. Walgreen's main rival, CVS Caremark Corp , does not report monthly sales.

(Reporting by Jessica Wohl; editing by John Wallace and Maureen Bavdek)