Did you know that powdered formula is not sterile in the can, so is not recommended at all for babies under one month of age, or for any baby at risk of infections? The manufacturers do not tell you this, but there have been babies who got very sick from the  Enterobacter sakazakii bacteria found in powered formula.

  I would stay with the concentrate or ready to feed if you must use formula.

 "Enterobacter sakazakii Infections Associated with the Use of Powdered Infant Formula --- Tennessee, 2001

Enterobacter sakazakii, a gram-negative, rod-shaped bacterium, is a rare cause of invasive infection with high death rates in neonates (1,2). This report summarizes the investigation of a fatal infection associated with E. sakazakii in a hospitalized neonate, which indicated that the infection was associated with the presence of the organism in commercial powdered formula fed to the infant. The implicated batch of formula has been recalled by the manufacturer. Clinicians should be aware of the potential risk for infection from use of nonsterile enteral formula in the neonatal health-care setting.

(from http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5114a1.htm)

FDA urges health care providers to report adverse events associated with the use of infant formulas as soon as possible to FDA's MedWatch program by calling their toll-free number (1-800-332-1088) or through the Internet (http://www.fda.gov/medwatch). Healthcare providers should report invasive disease in infants due to E. sakazakii, particularly bloodstream infection or meningitis with onset in the healthcare setting, to CDC's Division of Healthcare Quality Promotion (1-800-893-0485).

At the current time, FDA is determining if additional specific measures may be needed to assure the safe use of dried infant formulas in neonatal intensive care settings or by other vulnerable infant populations, and will communicate additional recommendations if and when they become available.

(from http://www.cfsan.fda.gov/~dms/inf-ltr3.html)