While proponents for better nurse-patient staffing ratios generally cite patient safety, studies also linked staffing improvements to reductions in injuries to healthcare workers.1-4

Nurses fighting to improve inadequate staffing levels at hospitals often cite patient safety, which holds a high moral ground while also speaking directly to the bottom-line concerns of the C-suite. As staff ratio laws are debated in various states, a new study might be presented as evidence of the issue.

Understaffing of registered nurses for two consecutive work shifts showed a statistically significant increase in healthcare-associated infections (HAIs), the researchers reported.5

“Clinically, it makes sense because if the understaffing is for only one shift, nurses can manage the workload,” says lead author Jingjing Shang, PhD, RN, associate professor at Columbia University School of Nursing in New York City. “However, if [the unit is understaffed] the whole day, the consequences will show up.”

Shang and colleagues examined “whether [HAIs] and nurse staffing are associated using unit-level staffing data.” Previous studies have suggested there is a link, but “the association between HAIs and nurse staffing are inconsistent and limited by methodological weaknesses,” the authors noted.

‘Significant Increase of the Infection Rate’

They analyzed data from a large urban health system between 2007 and 2012. HAIs were diagnosed using CDC definitions. To allow for the incubation period of pathogens, researchers assessed staffing levels two days before infection onset.

Overall, using a measure of patient-days, researchers 15% of patients “had one shift understaffed, defined as staffing below 80% of the unit median for a shift, and 6.2% had both day and night shifts understaffed. Patients on units with both shifts understaffed were significantly more likely to develop HAIs two days later,” the authors reported. The analysis included urinary tract infections, bloodstream infections, and pneumonia.

“If only one shift was understaffed, the risk was also high but not significant,” Shang says. “In the units that had both day and night shifts understaffed, we definitely saw this significant increase of the infection rate.”

The study also showed an increase in infection risk when units lacked support staff, such as licensed practical nurses and nurse assistants. The bottom line for hospital leaders is that dollars saved by cutting staffing will result in the expense and suffering of HAIs.

“In addition to their medical and financial impacts, HAIs also have psychological and social consequences for patients such as depression, anxiety, disability, and job loss,” Shang and colleagues emphasized.

Hospital administrators are the primary audience they wanted to reach with the paper, Shang says.

The threshold of 80% median unit staffing to define understaffing was drawn from previous research by the authors, serving as the line of demarcation between sufficient nursing levels and increased risk of HAIs.

As nurse staff levels decrease, the risks of cutting corners increase, resulting in lapses and breaches of infection control measures, such as hand hygiene and glove use.

Previous studies are limited in the way they assessed the effect of staffing on nursing, often averaging staffing over the whole hospital, Shang says. “They are not very specific on a unit level,” she says.

The authors of the Columbia study sought more precision on the unit and shift level, using payroll data to determine when the nurses clocked in and out, she says.

“The infections in our study are based on CDC definitions,” Shang says. “They are very precise, and are based on lab results, cultures, and symptoms. We measured the staffing very precisely, and the infections are based on clinical outcomes — not administrative data.”


  1. Leigh JP, Markis CA, Losif AM. California’s nurse-to-patient ratio law and occupational injury. Int Arch Occup Environ Health 2015;88:477-484.
  2. Clarke SP, Sloane DM, Aiken LH, et al. Effects of hospital staffing and organizational climate on needlestick injuries to nurses. Am J Public Health 2002;92:1115-1119.
  3. Gutsan E, Patton J, Willis WK, et al. Burnout syndrome and nurse-to-patient ratio in the workplace. Presented at the 54th Annual MBAA Conference, Chicago. Available at: https://bit.ly/2S2iL9b.
  4. Lipscomb J, Trinkoff A, Brady B, et al. Health care system changes and reported musculoskeletal disorders among registered nurses. Am J Public Health 2004;94:1431-1435.
  5. Shang J, Needleman J, Liu J, et al. Nurse Staffing and Healthcare-Associated Infection, Unit-Level Analysis. JONA 2019;49:260-265.