Case Study 6: P aeruginosa Outbreak in a Healthcare Setting

Healthcare-associated infections, previously referred to as nosocomial infections, are acquired by patients during their treatment in a healthcare setting. Healthcare-associated infections are of serious concern in the healthcare field. Hospitals are an ideal setting for opportunistic pathogens because they house both highly infectious and highly susceptible patients. Simple infection control practices such as handwashing and thorough cleaning and disinfecting of items have greatly reduced the incidence of healthcare-associated infections, yet such infections still occur. In the US alone, healthcare-associated infections are responsible for an estimated 2 million infections annually, 90,000 of which are fatal.

Most hospitals employ an infection control practitioner who monitors cases of disease throughout the hospital and ensures that proper hygiene and infection control procedures are followed. Additionally, many hospitals employ a hospital epidemiologist to assist the infection control practitioner in surveillance and epidemiologic investigations when necessary. The following case study examines what can happen when there is a lapse in surveillance and cases go unreported, and is loosely based on an actual outbreak that occurred in a children’s hospital in the United States.

You are the hospital epidemiologist at the regional children’s hospital in your state. You receive a call from the infection control practitioner, who was notified of a patient with early signs of a systemic infection by an attending physician in the neonatal intensive care unit (NICU). Despite a variety of differential diagnoses, the physician began antibiotic treatment, knowing that neonates like this patient are at high risk of developing neonatal sepsis. The physician ordered blood and serum samples, and requested that a sample of cerebrospinal fluid be collected as soon as possible. The infection control practitioner asks for your help in investigating this case.

You find out from the infection control practitioner that the patient is 2-week-old infant born prematurely at 33 weeks with underdeveloped lungs who has been intubated in the NICU since birth. The infant began showing signs of cyanosis and the nurse caring for the infant noticed that the child had a rapid heartbeat and a fever of 101.5°F.

After initial antibiotic treatment, the patient’s fever dropped to 100.8°F, but the heart rate remained elevated. A rapid laboratory test revealed gram-negative rods in the patient’s blood and cerebrospinal fluid, although specific lab results that will identify the pathogen are still pending. The finding of gram-negative rods in the blood is particularly worrisome and indicative of bacterial sepsis, but the infant appears to be responding well to the antibiotic treatment.

The physician reviews the chart of the mother to see if she could have been the source of the child’s infection. Although the baby was born prematurely, the mother showed no signs of infection upon admission to the hospital.

The infection control practitioner calls to tell you that laboratory diagnostic tests were positive for Pseudomonas aeruginosa (su-duh-mo-nas air-rudge-i-nosa). You both are immediately concerned about potential spread throughout the NICU and the rest of the hospital.

P. aeruginosa is the most common hospital-acquired pathogen and can cause severe infections in hospitalized patients. It occurs naturally in the environment, and can be found in soil, water, plants, and animals. P. aeruginosa is an opportunistic pathogen, meaning that it predominately infects persons with compromised immune systems. Infection with the bacteria can be localized or systemic if it enters the bloodstream. The National Nosocomial Infections Surveillance System published data collected from January 1986 through April 1997 showing that P. aeruginosa was the most common cause of healthcare-associated pneumonia in the ICU, being responsible for 17.4% of all cases. Outbreaks of P. aeruginosa have been linked to contaminated whirlpools; mattresses; antiseptics; tap water; respiratory, endoscopic, urodynamic, and pressure monitoring equipment; and even healthcare workers. P. aeruginosa infection is treatable, although acute infections in immunocompromised patients have resulted in a 30% – 60% mortality rate.

In looking over hospital surveillance data, you find an alarming trend that the new infection control practitioner did not notice. This case of is one of a growing number of P. aeruginosa infections in the NICU reported over the past year, and there have been several cases of P. aeruginosa this month.

Although there have been several cases other of P. aeruginosa infection throughout the hospital, the cases outside the NICU are comparable to baseline numbers and are not unusual. You begin to wonder if the NICU cases are linked to a common source and do some preliminary research on NICU patients in your hospital.

Since January of last year, 519 infants were admitted to the NICU with 439 staying longer than 48 hours, thus putting them at a higher risk of contracting the infection. Forty-six patients, including the most recent infant, were culture positive for P. aeruginosa. Despite the success in treating the most recent patient, 16 infected NICU patients died from their infection.