National Nosocomial Infections Surveillance System (NNIS)

About NNIS

The National Nosocomial Infections Surveillance (NNIS) system was developed in the early 1970s to monitor the incidence of healthcare-associated (nosocomial) infections (HAIs) and their associated risk factors and pathogens. NNIS is the only national system for tracking HAIs. The NNIS system is a cooperative, non-financial relationship between hospitals and CDC. This voluntary reporting system has grown from about 60 hospitals at inception to approximately 300 today. The NNIS system currently is undergoing a major redesign as a web-based knowledge management and adverse events reporting system that is scheduled to be available to participating NNIS hospitals in early 2005; all other U.S. hospitals, long-term-care facilities, and other healthcare organizations will be able to use the system by 2006. Once implemented, the redesigned system (to be called the National Healthcare Safety Network [NHSN]) will cover new areas of patient safety monitoring and evaluation.

CDC’s Division of Healthcare Quality Promotion manages the NNIS system and posts many of its publications on the Division’s website, including descriptions of participating hospitals and current trends in the types of adverse events that are monitored (see NNIS Reports on the NNIS publications page). A list of articles and chapters that contain information on NNIS methods and rationale for comparative rates is shown below.

Program Goals and Requirements

CDC developed the NNIS system to help infection control professionals and hospitals stay abreast of the rapidly expanding science and practice of infection prevention and control and better manage endemic and epidemic episodes of HAI. The principles of the NNIS system are based on CDC’s definition of public health surveillance and are divided into the following four objectives: a) detect and monitor adverse events, b) assess risk and protective factors, c) evaluate preventive interventions, and d) provide information to event reporters and stakeholders and partner with them to implement effective prevention strategies. The NNIS database is used to:

  • describe the epidemiology of HAIs
  • describe antimicrobial resistance associated with HAIs
  • produce aggregated HAI rates suitable for interhospital comparison.

CDC has required hospitals participating in NNIS to have sufficient a) infection control personnel to collect the data using standardized protocols and b) numbers of beds to yield enough cases of HAI for reliable estimation of the incidence and trends over time. The new NHSN will expand access to the system by dropping these human resource and bed-size requirements.

Data Uses and Confidentiality

CDC collects data on HAIs as part of its responsibility for research and investigation as authorized under Title III, Section 301, Section 304, and Section 306 of the Public Health Service Act (42 USC 241, 242b, 242k, and 242m(d)). Further, because of the sensitive nature of the data, the NNIS system has been granted a guarantee of confidentiality for the identities of both the patients and the reporting hospitals under Section 308(d) of the Public Health Service Act. Under these laws, CDC is permitted to analyze, interpret, and publish reports of aggregated data, but the agency is not allowed to release any patient-specific data, nor can it release any hospital-specific data without the express written consent of the participating hospital. The data are collected for the purposes of quality improvement and program management only. Hospitals are free to voluntarily release their own NNIS data to anyone they choose (e.g., to states or accrediting entities for accountability or for consumer choice purposes). The new web-based successor to NNIS, the NHSN, also a voluntary and confidential system, will assist a reporting hospital in releasing its data to organizations it selects (e.g., state or local health departments and quality improvement organizations).

NNIS measures are designed to minimize the burden of data collection and reporting by participating hospitals. The reliability of NNIS data depends on the assumption that the participating trained infection control professionals use standardized and validated NNIS data collection protocols and have no incentives to over- or underestimate their results in a voluntary, confidential system. However, data quality can be improved in either voluntary or mandatory systems by standard processes (e.g., independent audits and inter-rater reliability checks). The effectiveness of quality improvement in the NNIS system depends upon participants’ trust in the data for comparison across facilities or their use of the data for continuous quality improvement within their facilities.

Overall NNIS Methodology

Horan TC, Gaynes R. Surveillance of nosocomial infections. In: Mayhall CG, ed. Hospital epidemiology and infection control. Philadelphia: Lippincott Williams & Wilkins, 2004:1659-1702.

Accuracy of NNIS Data

Emori, TG, Edwards JR, Culver DH, et al. Accuracy of reporting nosocomial infections in intensive-care-unit patients to the National Nosocomial Infections Surveillance System: A pilot study. Infect Control and Hosp Epidemiol 1998;19:308-16.

Interhospital Rate Comparison Issues

Gaynes RP, Solomon S. Improving hospital-acquired infection rates: The CDC experience. J Qual Improvement 1996:22:457-67.

National Nosocomial Infections Surveillance System. Nosocomial infection rates for interhospital comparison: limitations and possible solutions. Infect Control Hosp Epidemiol 1991:609-12.

Surgical Site Infection Risk Indices

Culver DH, Horan TC, Gaynes RP, et al. Surgical wound infection rates by wound class, operative procedure and patient risk index. Am J Med 1991; 91(Suppl. 3B):152S-7S.

Haley RW, Culver DH, Morgan WM, et al. Identifying patients at high risk of surgical wound infection: a simple multivariate index of patient susceptibility and wound contamination. Am J Epidemiol 1985, 121:206-15.

Date last modified: February 16, 2005
Content source: 
Division of Healthcare Quality Promotion (DHQP)
National Center for Preparedness, Detection, and Control of Infectious Diseases