Monitoring Infections: Active vs. Passive Surveillance


Today, most HAI surveillance is passive, relying on data retrospectively gathered from medical records. Conversely, active surveillance involves prospective steps to identify patients who have or who may develop HAIs, using standardized definitions of infection, pre-determined criteria, and protocols that result in risk-adjusted HAI incidence rates.

By Cindi Crosby, PhD

For the past 20 years I have attended many conferences, both national and international, on the topic of healthcare-associated infections (HAIs). The fundamental debate still continues, however, as to the actual frequency of HAIs. Most infectious disease physicians, infection preventionists and epidemiologists agree that HAIs are under-reported. Why? Could it be in the way we conduct our surveillance?

Today, most HAI surveillance is passive, relying on data retrospectively gathered from medical records. Conversely, active surveillance involves prospective steps to identify patients who have or who may develop HAIs, using standardized definitions of infection, pre-determined criteria, and protocols that result in risk-adjusted HAI incidence rates.

Implementing and maintaining an active surveillance system requires personnel and financial resources, and so its often crucial to justify the investment with improved patient outcomes. Outcomes may then be used to develop targeted intervention programs. At a high level:
Active surveillance may be most directly associated with monitoring and controlling the risk of outbreaks of drug-resistant pathogens, such as methicillin-resistant Staphylococcus aureus (MRSA).
Increasingly, active surveillance has been used to identify patients at high risk for infections associated with surgery and hospitalization in intensive care units (ICUs). 

Here are several more detailed examples of published outcomes from active surveillance programs:

Active surveillance to decrease MRSA isolates
Healthcare institutions are acutely aware of the rise in drug-resistant pathogens. In 1980, MRSA accounted for about 2 percent of all S. aureus HAIs. By 2006, it accounted for more than 60 percent.1 In response, some hospitals initiated active surveillance testing of patients considered high-risk for active MRSA infections or colonization. One hospital system using passive and ICU-targeted surveillance recorded no change in MRSA isolates over a three-year period. They implemented an active surveillance program to universally screen all patients upon admission for nasal colonization with MRSA.2 Patients found to be colonized received treatment with mupirocin nasal ointment and periodic bathing with antisepsis soap. For each year after initiation of active universal screening, the hospital recorded decreases in MRSA and total S. aureus clinical isolates compared to each of the prior three years of passive surveillance (P < 0.0001). The author of this study suggests that the decrease in MRSA isolates correlates with decreased disease.

Active surveillance to decrease surgical site infections
Active surveillance may be particularly useful in identifying surgical site infections (SSIs), which can develop up to 30 days after a patient is discharged. In one study of SSI rates identified passively by neurosurgeons,surgeons missed 36 percent of SSIs using passive surveillance, as evidenced by results from active surveillance performed by infection control professionals.3 Under-reporting HAIs with passive surveillance has been shown to be more likely among certain types of surgical patients during the post-discharge period. In a Dutch study of post-discharge SSI rates for various surgeries, more SSIs were identified with a recommended active surveillance protocol (43 percent) than with passive surveillance (25 percent).4  This study also demonstrated that for common surgeries including appendectomy, knee prosthesis surgery, mastectomy and hysterectomy, most SSIs developed after discharge and were underestimated when passive surveillance was used.

Active surveillance of device-associated infections
Patients at risk for device-associated infections such as catheter-associated urinary tract infections (CAUTIs) and ventilator-associated pneumonia (VAP) may benefit from active surveillance designed to identify risk factors that are unique to a particular patient population or hospital unit. An active surveillance program undertaken at Alexandria University Hospital in Egypt included an objective to identify etiologic and antibiotic resistance patterns associated with CAUTIs in the facilitys four ICUs.5 During a 13-month study period, 757 patients in the ICU who had existing urinary catheters or who were catheterized after ICU admission were monitored. The overall infection rate was 15.7 CAUTIs per 1,000 catheter days, with the following risk factors identified:
Female gender
Previous catheterization within the same hospital admission
Admission to the chest unit
Patient age 40 or older
Prolonged duration of catheterization
Prolonged hospital and ICU stay

In addition, the pathogen profile was identified, including Candida (51 percent), Gram-negative pathogens (33.5 percent), and Gram-positive organisms (15.4 percent). The prevalence of extended-spectrum beta-lactamase-producing organisms included E. coli (78.6 percent) and K. pneumoniae (56 percent). Investigators concluded that existing infection control policies were inadequate, and a tailored intervention to address these specific risk factors and microorganisms is now being designed.
Active surveillance was also used to guide evidence-based VAP prevention strategies in one tertiary medical-surgical trauma ICU in Saudi Arabia.6 VAP cases were diagnosed according to predefined criteria, and VAP microbiology, risk factors, and outcomes were recorded. The intervention program resulted in a decrease in VAP infection from 19.1 to 6.3 per 1,000 ventilator days from 2003 to 2009.  Active surveillance identified the following risk factors for VAP:
Accidental extubation
Trauma versus medical diagnosis
Chronic obstructive pulmonary disease
Neuromuscular blockade

The most common isolated pathogens were Gram-negative organisms. Investigators realized a reduction in VAP rates with active surveillance, reporting, and evidence-based preventive strategies and identified modifiable risk factors to be included in additional interventions.
Of note, another active surveillance testing program designed to identify MRSA colonization and institute contact isolation of affected patients in two Michigan hospitals also resulted in a decrease in VAP in both hospitals, although MRSA infection decreased in only one hospital.7 The investigators concluded that active surveillance testing with contact precautions was effective in reducing both VAP and MRSA in their facilities.

Economic consequences of surveillance
These studies are just a few examples of successful active surveillance programs that resulted in reduced infection rates. But even if active surveillance is shown to improve patient outcomes, are we prepared to actively capture HAI data? I would speculate that many institutions are not. A common objection to implementing active surveillance is the cost of labor and economic resources, particularly during a time when healthcare institutions are under pressure to reduce the cost of care. Those providers who are not taking steps to lower the risk and incidence of HAIs, however, may be taking an even greater financial risk.  Extended lengths of stay, antibiotic days, and readmissions are costly and create longer-term economic pressure. In a study by Dimick et al. (2004), median total hospital costs for patients with and without post-operative infection alone were $13,083 vs. $ 5,044, a statistically significant result.8

The difference between passive and active surveillance may seem like an academic debate among infection control professionals, but the consequences in terms of patient morbidity and costs of care are real and affect everyone. 

Cindi Crosby, PhD, is vice president of global medical affairs for CareFusion. The author wishes to acknowledge Catherine M. Jarrell, MA, medical affairs consultant at CareFusion, for providing medical writing assistance.

1. Hall G, Flayhart D. Active surveillance culture as a promising new tool. Infection Control Today. Available at: Accessed on February 15, 2012.
2. Hacek DM, Paule SM, Thomson RB Jr, Robicsek A, Peterson LR. Implementation of a universal admission surveillance and decolonization program for methicillin-resistant staphylococcus aureus (MRSA) reduces the number of MRSA and total number of S. aureus isolates reported by the clinical laboratory. J Clin Microbiol. 2009;47:3749-52.
3. Heipel D, Ober JF, Edmond MB, Bearman GM. Surgical site infection surveillance for neurosurgical procedures: a comparison of passive surveillance by surgeons to active surveillance by infection control professionals. Am J Infect Control. 2007;35:200-2.
4. Manniën J, Wille JC, Snoeren RLMM, van den Hof S. Impact of postdischarge surveillance on surgical site infection rates for several surgical procedures: results from the Nosocomial Surveillance Network in The Netherlands. Infect Control Hosp Epidemiol. 2006:27:809-16.
5. Talaat M, Hafez S, Saied T, et al. Surveillance of catheter-associated urinary tract infection in 4 intensive care units at Alexandria university hospitals in Egypt. Am J Infect Control. 2010;38:222-8.
6. Al-Dorzi HM, El-Saed A, Rishu AH, et al. The results of a 6-year epidemiologic surveillance for ventilator-associated pneumonia at a tertiary care intensive care unit in Saudi Arabia. Am J Infect Control. 2012. [Epub ahead of print]
7. Martinez-Capolino C, Reyes K, Johnson L, et al. Impact of active surveillance on meticillin-resistant Staphylococcus aureus transmission and hospital resource utilisation. J Hosp Infect. 2010;74(3):232-7. 
8. Dimick JB, Chen SL, Taheri PA, Henderson WG, Khuri SF, Campbell DA Jr. Hospital costs associated with surgical complications: a report from the private-sector National Surgical Quality Improvement Program. J Am Coll Surg. 2004;199:531-7.


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