Hospital Sink Drains: A Hidden Bacteria Hotspot Despite Cleaning

Researchers from Spain conducted a study on sink drains across various wards in a contemporary university hospital that follows advanced cleaning protocols. By employing culturing techniques and DNA barcoding, they identified 67 distinct bacterial species.

Among these were Klebsiella, Enterobacter, and Pseudomonas aeruginosa, which are well-known for their ability to cause infections associated with healthcare settings. Some of the strains discovered exhibited resistance to current antibiotics, including cephalosporins and carbapenems. Consequently, sink drains seem to act as reservoirs for both recognized and emerging pathogens of significant concern.

When people are hospitalized, they expect to receive treatment and recover. However, it is not uncommon to contract new infections during the stay. These ‘healthcare-associated infections’ (HAIs) are an escalating issue globally, consuming an estimated 6% of hospital budgets worldwide.

In the European Union, HAIs account for over 3.5 million cases annually, leading to 2.5 million disability-adjusted life years lost, a financial burden of up to €24 billion, and approximately 90,000 fatalities. They rank as the sixth leading cause of death in the United States as well.

Patients with weakened immune systems, combined with inadequate adherence to hygiene practices in some hospitals, create an environment conducive to HAIs. Additionally, the extensive use of antibiotics in healthcare settings tends to favor the emergence of resilient bacterial strains.

When resistance genes are located on mobile genetic elements, they can transfer between different bacterial species, potentially resulting in new diseases.

Here we show that hospital sink drains host bacterial populations that change over time, despite impeccable cleaning protocols in the particular hospital we looked at. These results highlight that controlling bacterial growth in drains, and preventing colonization by new strains of such hard-to-disinfect niches, is likely a global problem.”

Dr. Margarita Gomila, Professor and Study Senior Author, University of the Balearic Islands

The study was published in Frontiers in Microbiology.

Rigorous Cleaning Protocols

Gomila and her team concentrated on sink drains within a modern university hospital on the island of Majorca. The hospital, established in 2001, is operated by the health service of the Balearic Islands.

The cleaning protocols implemented are cutting-edge: sinks and drains are regularly cleaned with bleach and disinfected with chemicals and pressurized steam every two weeks, or monthly in non-patient areas. Additionally, drainpipes undergo hyperchlorination at low temperatures once a year.

Between February 2022 and February 2023, they collected samples using cotton swabs from six drains in each of five wards: two intensive care units, including a newly opened one; one ward each for hematology, short stays, and general medicine; as well as a microbiology lab. The sampled bacteria were cultured on five different media at two distinct temperatures, and the resulting 1,058 isolates were identified using DNA barcoding and mass spectrometry. An automated platform was then utilized to assess the resistance of 219 isolates to a variety of antibiotics.

The researchers identified 67 unique species from the drains. The diversity of bacteria in most drains fluctuated over time without any discernible pattern, seasonal or otherwise. The highest diversity was observed in general medicine and intensive care wards, while the microbiology laboratory had the fewest isolates.

Notably, the newly established intensive care unit, which opened in July 2022, exhibited a significant level of bacterial diversity from the outset, comparable to that of its longer-established counterpart.

Dominating the wards were six species of Stenotrophomonas and Pseudomonas aeruginosa, a pathogen recognized for causing ventilator-associated pneumonia and sepsis, and classified by the WHO as one of the most significant threats to human health regarding antibiotic resistance.

At least 16 additional Pseudomonas species were detected at various times and in different wards, particularly in the short-stay ward.

Other well-known pathogens associated with hospitals that were frequently identified include Klebsiella pneumoniae in the general medicine ward, Acinetobacter johnsonii and Acinetobacter ursingii in both general medicine and intensive care units, Enterobacter mori and Enterobacter quasiroggenkampii in the short-stay ward, and Staphylococcus aureus in intensive care and hematology departments.

The bacteria we found may originate from many sources, from patients, medical personnel, and even the environment surrounding the hospital. Once established in sink drains, they can spread outwards, posing significant risks to immunocompromised patients above all.”

Dr. Margarita Gomila, Professor and Study Senior Author, University of the Balearic Islands

Antibiotic Resistance

Among the identified species, Klebsiella, Enterobacter, and P. aeruginosa are part of the ESKAPE group, which is recognized for thriving in hospital environments and exhibiting frequent multi-drug resistance along with a high potential for causing infections.

In this study, 21% of P. aeruginosa isolates demonstrated resistance to at least one antibiotic class. Several strains of Klebsiella and Enterobacter were found to be resistant to the third-generation cephalosporins, yet they remained susceptible to the carbapenems that are typically employed against multidrug-resistant infections.

Alarmingly, the blaVIM gene, which confers resistance to carbapenems, was sporadically identified in a small number of P. aeruginosa strains from the two intensive care units, the general medicine ward, and the short-stay ward.

The researchers concluded that hospital drainage systems can act as reservoirs for both established and emerging pathogens, some of which display significant antibiotic resistance.

Cleaning protocols are important and should be frequently applied, especially in wards that are kept separate precisely to slow the spread of potentially harmful bacteria. But to get to the bottom of the problem, it is essential to study the source of these bacteria and their routes of transmission.”

José Laço, PhD Student and Study First Author, University of the Balearic Islands