In the October 30, 2009, edition of its weekly MMWR publication, the Centers for Disease Control and Prevention (CDC) reported on an investigation in November, 2008, when Cronobacter sakazakii bacteria was isolated in two different infants.[1]  As recognized by the CDC, isolation of this organism from human specimens is rare and makes these cases notable.  Cronobacter sakazakii (formerly Enterobacter sakazakii) are rare causes of infant septicemia and meningitis, resulting in death in approximately 40% of cases. Since 1958, 120 cases of Cronobacter sakazakii infection in infants have been reported, an average of fewer than three cases per year worldwide. Powdered infant formula, which is not sterile, has been implicated repeatedly as a vehicle of Cronobacter infection. This new report provides important additional information regarding this elusive pathogen, and updates the CDC’s recommendations regarding safer powdered infant formula preparation, storage, and handling. This report also reasserts the continuing hazards to infants created by powdered infant formula contaminated with the Cronobacter sakazakii pathogen. Cronobacter sakazakii is a foodborne pathogen that can cause sepsis, meningitis, or necrotizing enterocolitis in newborn infants, particularly premature infants or other infants with weakened immune systems. Over the last several years, investigations of several outbreaks of Cronobacter sakazakii infection occurring in neonatal intensive care units worldwide have shown the outbreaks to be associated with milk-based powdered infant formulas. On March 29, 2002, Mead Johnson Nutritionals, Evansville, Indiana, issued a Press Release stating, “…in keeping with our commitment to provide safe and healthy nutritional products, is recalling one batch of Portagen powder.”  Portagen powder is a nutritional product for adults, toddlers and infants with rare digestive diseases that prevent them from digesting or absorbing fats. The Press Release stated that, “The recall was initiated after a report that a premature infant died in April 2001, of a rare form of meningitis caused by the bacteria Enterobacter sakazakii. The child reportedly became ill after being tube-fed Portagen from this batch.” A few days later, on April 11, 2002, FDA for the first time issued a national alert to health care professionals about the risk of Cronobacter sakazakii infections in hospitalized newborn infants, particularly premature infants or other immuno-compromised infants fed powdered infant formulas.  The alert was based on the findings of the CDC investigation on the fatal Cronobacter sakazakii meningitis case associated with the consumption of Portagen in the neonatal intensive care unit in Tennessee in April 2001. The details of CDC’s investigation were outlined in the April 12, 2002, edition of the Morbidity and Mortality Weekly Report (MMWR).[2] According to the CDC, the use of milk-based powdered formula was a likely factor in the fatal infection of the infant. As part of their investigation, CDC performed a survey on all 49 infants in the neonatal intensive care unit and intermediate nursery during April 10 – 20, 2001.  CDC colonized Cronobacter sakazakii from nine infants. One 11-day-old male who was already seriously ill acquired Cronobacter sakazakii meningitis and died.  Two infants exhibited respiratory distress, one infant had genitourinary symptoms but recovered, and the remaining five cases showed no symptoms.  Comparing cases to non-cases, only exposure to powdered infant formula was a significant risk factor. Significantly, cultures from both opened and unopened cans of powdered formula were later found positive at very low levels for Cronobacter sakazakii. This case provided clear evidence, for the first time in the United States, of an association between a Cronobacter sakazakii illness and the consumption of contaminated powdered infant formula.  As a result, during the summer of 2002, the FDA conducted a field survey of formulas produced by each major domestic powdered infant formula manufacturer, to determine the prevalence of Cronobacter sakazakii in these products.  Official samples were taken from raw materials and from selected powdered infant formula finished products.  Twenty two samples of finished product were tested, and 22.7% of the samples tested positive for Cronobacter sakazakii.[3] The FDA then issued a revised letter to health professionals, which again provided its recommendations for minimizing the risk in those circumstances when a powdered infant formula had to be used for premature or immune-compromised infants.[4]  The FDA pointed out that powdered infant formulas are not commercially sterile products. Powdered milk-based infant formulas are heat-treated during processing, but unlike liquid infant formula products they are not subjected to high temperatures for sufficient time to make the final packaged product commercially sterile.  The letter further stated that, “In light of the epidemiological findings and the fact that powdered infant formulas are not commercially sterile products, FDA recommends that powdered infant formulas not be used in neonatal intensive care settings unless there is no alternative available.”  Finally, if the only option available to address the nutritional needs of a particular infant was a powdered formula, the FDA recommended preparation steps to reduce the risk of infection. In August 2006, two CDC medical epidemiologists published findings their literature review and analysis of 46 cases of invasive infant Cronobacter sakazakii infection.[5] Their intent was to more clearly define the host risk factors and disease course and to further refine prevention and treatment efforts.   Twelve infants had bacteremia, 33 had meningitis, and 1 had a urinary tract infection. Among meningitis patients, 11 (33%) had seizures, 7 (21%) had brain abscess, and 14 (42%) died. Twenty-four (92%) of 26 infants with feeding patterns specified were fed powdered formula. Formula samples associated with 15 (68%) of 22 cases yielded E. sakazakii; in 13 cases, clinical and formula strains were indistinguishable. The authors found that further clarification of clinical risk factors and improved powdered formula safety measures were necessary. In its most recent related 2009 CDC report, the article states that the Cronobacter sakazakii bacteria were isolated from two non-hospitalized, unrelated infants in November 2008, in New Mexico.  CDC and FDA investigators determined that the female infant had been infected with Cronobacter sakazakii, and that the male infant had been colonized with Cronobacter sakazakii, without clear evidence of infection.  Ingestion of powdered infant formula was the only identified risk factor for Cronobacter sakazakii exposure for the two infants. The two infants had consumed the same brand of powdered infant formula but had no other common exposures. The female infant had documented Cronobacter sakazakii infection that led to severe brain injury and hydrocephalus.  Although a Cronobacter sakazakii organism was isolated from the male infant at autopsy, the role of that organism in the infant’s apparent death from SIDS is unknown. The two infants had consumed the same brand of formula, but their clinical Cronobacter sakazakii isolates had different Pulsed Field Gel Electrophoresis (PFGE) patterns. None of the samples obtained from the home of the female infant yielded Cronobacter sakazakii.  Samples taken from the home of the male infant, however, provided positive results for Cronobacter sakazakii.  An opened can of powdered infant formula yielded a Cronobacter sakazakii isolate with a PFGE pattern that was indistinguishable from the clinical Cronobacter sakazakii isolate from the male infant.  Additionally, the vacuum cleaner filter from the home of the male infant also yielded Cronobacter sakazakii, but with a different PFGE pattern than the PFGE pattern isolated in both the male infant and the open powdered infant formula can. The CDC reaffirmed in this report that prior investigations have found Cronobacter sakazakii cultured from prepared formula, unopened powdered infant formula containers, and the environment where powdered infant formula was reconstituted, clearly implicating powdered infant formula as the source of outbreaks. Other than an improperly prepared intravenous nutrition solution implicated in one outbreak, no other clear source of Cronobacter sakazakii infection has been identified to date. Accordingly, the report again recommended that preparers should be aware that powdered infant formula is not sterile and can contain pathogenic organisms, such as Cronobacter sakazakii.  The report also recommended that WHO guidelines for preparation of powdered infant formula, including reconstitution with water hot enough to inactivate Cronobacter sakazakii, be adopted,  for safer powdered infant formula preparation, storage, and handling. In the United States and elsewhere, present recommendations are: to breastfeed infants when possible; to use sterile liquid infant formula in high-risk settings (e.g., neonatal intensive-care units and hospital nurseries); and to adhere to the safest available powdered infant formula preparation procedures.  Interestingly, the CDC report noted that the manufacture of sterile powdered infant formula, perhaps by using irradiation in combination with other techniques, could prevent infant disease.  Finally, the CDC stated that further precautions to prevent extrinsic contamination of powdered infant formula are needed, including the engineering of powdered infant formula packaging to prevent introduction of bacteria through contaminated hands, scoops, or other items. Pictured:  This trypticase soy agar plate culture of E. sakazakii is showing mucoid flat colonies after three days growth at 25° C.  Photo credit:  CDC/Dr. J. J. farmer REFERENCES 1. “Cronobacter Species Isolation in Two Infants- New Mexico, 2008“, MMWR, October 30, 2009 / 58(42); 1179-1183 2.  “Enterobacter sakazakii Infections Associated with the Use of Powdered Infant Formula – Tennessee, 2001“, MMWR, April 12, 2002 / Vol. 51 / No. 14 3.  “FDA Field Survey of Powdered Formula Manufacturing”, Zink, Don L., Ph.D., FDA, Power Point presentation. 4.  “Health Professionals Letter on Enterobacter sakazakii Infections Associated With Use of Powdered (Dry) Infant Formulas in Neonatal Intensive Care Units“, FDA/CFSAN, April 11, 2002: Revised October 10, 2002. 5. Bowen AB, Braden CR, “Invasive Enterobacter sakazakii disease in infants“, Emerg Infect Dis, August 2006.