KANSAS CITY, MO—Infestation of wounds with maggots (myiasis) occurs periodically in large hospitals, especially during the summer. Nasal myiasis is much less common, and one of the few known causes is the green blowfly (Phaenicia sericata). In 1998, nasal myiasis with P sericata occurred in two intubated patients at the Veterans Affairs Medical Center in Kansas City, Missouri.[1]

These infestations, at first attributed to flies that randomly came into the hospital via open areas, were later found to be caused by flies that entered the hospital in response to the presence of large numbers of mouse carcasses. Arriving at this conclusion required considerable detective work, but the investigation provided a valuable lesson in unintended consequences: Reductions in hospital support staffing had led to a mouse infestation.

The first patient was a 45-year-old man who was admitted into the intensive care unit (ICU) on July 12, 1998, with cardiomyopathy. On July 22, a nurse noticed oral and nasopharyngeal maggots. Cavities were irrigated and the larvae were removed. No attempt was made to identify the maggots.

The second patient was a 49-year-old man who was admitted to the ICU with cardiogenic shock on September 22, 1998. On September 30, maggots were noticed around the purulent drainage from the nasotracheal tube. The larvae, along with adult flies found in the ICU, were sent to the Department of Entomology at the University of California, Riverside, for identification.

The medical ICU in which both patients were treated was new; it had been in use for only seven months when the first case of nasal myiasis occurred. Shortly after the medical ICU was opened, construction began on a new surgical ICU nearby. The first case was initially thought to be caused by flies entering open windows during the two units’ construction. Electrical insect lights were installed in response, but numerous flies were still seen throughout the hospital.

Coincident with this construction was a massive house mouse inhabitation. Mouse bait and glue traps were placed throughout the hospital. Afterward, mice and flies were observed in large numbers on all hospital floors. The second case of nasal myiasis occurred at this time.

In an interview with RESPIRATORY REVIEWS, Stephen Klotz, MD, one of the report’s coauthors, explained how he and his colleagues made the connection between myiasis and mice. “In the first patient, I assumed the flies were just trapped indoors. The connection was made with the second patient. I sent the flies to an entomologist, who asked if we didn’t have a rodent problem. And we definitely had a rodent problem.”

The maggots and adult flies were identified as P sericata. On learning the identity of the flies and their egg-laying habits, aerosolization of the ICU was performed. All bait and glue traps were removed and replaced with live traps. In two months, 184 mice were caught, and there were no further episodes of nasal myiasis.

Dr. Klotz, now a Professor of Infectious Diseases at the University of Arizona in Tucson, noted that the construction work had nothing to do with the flies. “The flies were being drawn into the hospital by the presence of mouse carcasses—where they wanted to lay their eggs.” Once trapped inside the ICU, the flies were forced to lay their eggs in patients’ nasal discharge.

Incidentally, one year later, an outbreak of P sericata occurred in the operating department. After a careful search of the surrounding area, seven mouse carcasses were found on glue boards that had not been removed the previous year.

The mouse problem developed following reductions in hospital support staff personnel. Because of these reductions, food was not being stored properly in the hospital’s cafeteria and canteen, and many food preparation work areas were not being cleaned properly.

Ronald Sherman, MD, MSc, an Assistant Professor of Medicine at the University of California at Irvine, published a study in 2000 of the incidence of wound myiasis and its clinical causes.[2] When tracing the origin of a myiasis occurrence, Dr. Sherman explained, “The first and foremost obligation is to identify the maggot. Only by identifying the species and age of the maggot is it possible to determine the approximate time of infestation. Once the time of infestation is determined, it is a relatively simple matter to determine where the patient was at that time.”

Dr. Sherman believes that the incidence of myiasis in hospital patients is underreported. He points out that “for hospital-acquired myiasis, it is particularly difficult to obtain data because hospitals are understandably reluctant to publicize such occurrences. Unfortunately, by not making known the frequency of hospital-acquired myiasis, we create the misconception that it is a much more rare, and therefore, much more medically reprehensible event than it really is.”

—Gale Jurasek