National Nosocomial Infections Surveillance (NNIS) System Report, data summary from January 1992 through June 2004, issued October 2004

Article Outline

• Adult and pediatric ICU surveillance component
• HRN surveillance component
• Surgical patient surveillance component
• Appendix A. Defined daily dose (DDD) of antimicrobial agents, by class and group
• Appendix B
  • How to calculate a device-associated infection rate and device utilization ratio with ICU and HRN component data
• Appendix C
  • Interpretation of percentiles of infection rates or device utilization ratios
• Appendix D
  • CDC NNIS PERSONNEL
• References
• Copyright

This report is a summary of the data collected and reported by hospitals participating in the National Nosocomial Infections Surveillance (NNIS) System from January 1992 through June 2004 and updates previously published data.^1., ^2., ^3., ^4.

The NNIS System was established in 1970 when selected hospitals in the United States routinely began reporting their nosocomial infection surveillance data for aggregation into a national database. Hospitals participating in the NNIS System provide general medical-surgical inpatient services to adults or children requiring acute care. Identity of the nearly 300 hospitals currently participating in the NNIS System is confidential.

All NNIS data are collected using standardized protocols, called “surveillance components”: adult and pediatric intensive care unit (ICU), high-risk nursery (HRN), and surgical patient.^5., ^6., ^7. The components may be used singly or simultaneously, but once selected, they must be used for a minimum of 1 calendar month. All infections are categorized into major and specific infection sites using standard CDC definitions that include laboratory and clinical criteria.⁶

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Adult and pediatric ICU surveillance component 

Infection control professionals (ICPs) collect data on all sites of nosocomial infection in patients located in ICUs, as well as ICU-specific denominator data. Site-specific infection rates can be calculated by using as a denominator the number of patients at risk, patient-days, and days of indwelling urinary catheterization, central vascular cannulation (central line), or ventilation.

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HRN surveillance component 

ICPs collect data on all sites of nosocomial infection in patients located in HRN, and HRN-specific denominator data. Site-specific infection rates can be calculated by using as a denominator the number of patients at risk, patient-days, and days of umbilical catheter/central line use or ventilation for each of 4 birth-weight categories (≤1000 gm, 1001–1500 gm, 1501–2500 gm, and ≥2500 gm).

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Surgical patient surveillance component 

ICPs select from the NNIS operative procedure list those procedures they wish to follow up and monitor the patients undergoing those procedures for all infections or surgical site infections (SSI) only. A record on every patient undergoing the selected procedure is generated that includes information on risk factors for SSI such as wound class,⁸ duration of operation, and American Society of Anesthesiology (ASA) score.⁹ Using a composite index for predicting the risk of SSI after operation, ICPs can calculate rates by the number of risk factors present.⁴

The time periods for the data contained in this report vary depending on the table. Each table represents NNIS data from one of the surveillance components. For the ICU and HRN surveillance components where data volume was large after risk stratification, we were able to construct tables comprised of data from fewer and more recent years only (January 2002 through June 2004; Table 1, Table 2, Table 3, Table 4). However for the surgical patient component, we had to use all the data from January 1992 through June 2004, because the numbers of operations in each procedure-risk-stratum was too small to produce stable rates when only more recent years' data were used (Table 5, Table 6, Table 7, Table 8). Similarly, Table 9, Table 10 required use of data reported since January 1998 through June 2004.

Table 1. Pooled means and percentiles of the distribution of device-associated infection rates, by type of ICU, ICU component, January 2002 through June 2004

Urinary catheter-associated UTI rate∗				Percentile
Type of ICU	No. of units	Urinary catheter-days	Pooled mean	10%	25%	50% (median)	75%	90%
Coronary	60	170,759	4.5	0.8	2.6	4.0	7.5	10.2
Cardiothoracic	48	193,424	3.0	0.0	1.1	2.4	3.9	6.2
Medical	94	448,161	5.1	0.7	2.5	4.7	7.1	9.5
Medical-surgical
Major teaching	99	593,100	3.9	1.3	2.1	3.3	5.2	7.5
All others	108	757,531	3.3	0.6	1.6	3.1	5.1	6.9
Neurosurgical	29	99,039	6.7	1.8	3.1	6.0	7.8	9.5
Pediatric	52	104,788	4.0	0.0	1.6	3.6	6.1	8.1
Surgical	99	486,575	4.4	1.4	2.3	3.8	6.5	8.8
Trauma	22	104,181	6.0	2.1	3.8	5.7	7.3	9.3
Burn	14	44,342	6.7	—	—	—	—	—
Respiratory	6	17,784	6.4	—	—	—	—	—

Central line-associated BSI rate†				Percentile
Type of ICU	No. of units	Central line-days	Pooled mean	10%	25%	50% (median)	75%	90%
Coronary	60	116,546	3.5	1.0	1.5	3.2	7.0	9.0
Cardiothoracic	48	182,407	2.7	0.0	0.9	1.8	2.7	4.9
Medical	94	312,478	5.0	0.5	2.4	3.9	6.4	8.8
Medical-surgical
Major teaching	100	430,979	4.0	1.7	2.6	3.4	5.1	7.6
All others	109	486,115	3.2	0.8	1.6	3.1	4.3	6.1
Neurosurgical	30	56,645	4.6	0.0	0.9	3.1	5.8	10.6
Pediatric	54	161,314	6.6	0.9	3.0	5.2	8.1	11.2
Surgical	99	358,578	4.6	0.0	2.0	3.4	5.9	8.7
Trauma	22	70,372	7.4	1.9	3.3	5.2	8.2	11.9
Burn	14	43,002	7.0	—	—	—	—	—
Respiratory	6	12,593	4.8	—	—	—	—	—

Ventilator-associated pneumonia rate‡				Percentile
Type of ICU	No. of units	Ventilator-days	Pooled mean	10%	25%	50% (median)	75%	90%
Coronary	59	76,145	4.4	0.0	1.9	4.0	6.8	9.8
Cardiothoracic	47	98,358	7.2	1.2	2.9	6.3	12.6	15.5
Medical	92	268,518	4.9	0.5	2.1	3.7	6.2	8.9
Medical-surgical
Major teaching	99	320,916	5.4	1.2	2.6	4.6	7.2	9.9
All others	109	351,705	5.1	1.7	2.9	5.1	6.7	8.9
Neurosurgical	29	45,073	11.2	0.0	2.4	6.2	13.5	16.8
Pediatric	52	133,995	2.9	0.0	0.9	2.3	4.8	8.1
Surgical	98	253,900	9.3	2.2	4.7	8.3	12.2	17.9
Trauma	22	63,137	15.2	4.3	8.0	11.4	16.6	25.3
Burn	14	23,117	12.0	—	—	—	—	—
Respiratory	6	18,838	4.9	—	—	—	—	—

UTI, Urinary tract infection; BSI, bloodstream infection.

Table 2. Pooled means and percentiles of the distribution of device utilization ratios, by type of ICU, ICU component, January 2002 through June 2004

Urinary catheter utilization∗				Percentile
Type of ICU	No. of units	Patient-days	Pooled mean	10%	25%	50% (median)	75%	90%
Coronary	60	305,911	0.56	0.26	0.46	0.60	0.70	0.78
Cardiothoracic	48	230,487	0.84	0.58	0.76	0.88	0.95	0.96
Medical	94	596,588	0.75	0.58	0.65	0.76	0.83	0.88
Medical-surgical
Major teaching	99	759,464	0.78	0.65	0.74	0.82	0.87	0.90
All others	108	979,550	0.77	0.67	0.73	0.78	0.84	0.87
Neurosurgical	29	116,931	0.85	0.65	0.76	0.82	0.92	0.95
Pediatric	53	349,258	0.30	0.11	0.20	0.30	0.41	0.47
Surgical	99	590,220	0.82	0.65	0.76	0.86	0.92	0.96
Trauma	22	115,099	0.91	0.77	0.85	0.93	0.96	0.98
Burn	14	76,877	0.58	—	—	—	—	—
Respiratory	6	26,567	0.67	—	—	—	—	—

Central line utilization†				Percentile
Type of ICU	No. of units	Patient-days	Pooled mean	10%	25%	50% (median)	75%	90%
Coronary	60	305,911	0.38	0.15	0.22	0.36	0.51	0.60
Cardiothoracic	48	230,487	0.79	0.55	0.70	0.83	0.87	0.93
Medical	95	596,588	0.52	0.31	0.37	0.52	0.64	0.75
Medical-surgical
Major teaching	100	759,464	0.57	0.36	0.47	0.56	0.66	0.74
All others	109	979,550	0.50	0.29	0.38	0.49	0.58	0.66
Neurosurgical	30	116,931	0.48	0.23	0.33	0.50	0.55	0.65
Pediatric	54	349,258	0.46	0.20	0.31	0.46	0.57	0.64
Surgical	100	590,220	0.61	0.34	0.52	0.63	0.72	0.81
Trauma	22	115,099	0.61	0.40	0.49	0.60	0.71	0.79
Burn	14	76,877	0.56	—	—	—	—	—
Respiratory	6	26,567	0.47	—	—	—	—	—

Ventilator utilization‡				Percentile
Type of ICU	No. of units	Patient-days	Pooled mean	10%	25%	50% (median)	75%	90%
Coronary	60	305,911	0.25	0.11	0.14	0.23	0.36	0.41
Cardiothoracic	48	230,487	0.43	0.25	0.31	0.40	0.48	0.58
Medical	94	596,588	0.46	0.22	0.32	0.46	0.57	0.67
Medical-surgical
Major teaching	99	759,464	0.43	0.23	0.32	0.43	0.55	0.62
All others	109	979,550	0.37	0.22	0.28	0.35	0.42	0.52
Neurosurgical	29	116,931	0.39	0.19	0.26	0.34	0.45	0.56
Pediatric	52	349,258	0.39	0.17	0.25	0.36	0.49	0.57
Surgical	99	590,220	0.44	0.19	0.31	0.46	0.53	0.65
Trauma	22	115,099	0.56	0.39	0.44	0.50	0.67	0.77
Burn	14	76,877	0.31	—	—	—	—	—
Respiratory	6	26,567	0.71	—	—	—	—	—

Table 3. Pooled means and percentiles of the distribution of device-associated infection rates, by birth-weight category, HRN component, January 2002 through June 2004

BSI, Bloodstream infection.

Table 4. Pooled means and percentiles of the distribution of device utilization ratios, by birth-weight category, HRN component, January 2002 through June 2004

Table 5. SSI rates^∗, by operative procedure and risk index category, Surgical Patient component, January 1992 through June 2004

CBGB, Coronary artery bypass graft with chest and donor site incisions (eg, femoral or radial artery harvested as donor vessel for bypass graft); CBGC, coronary artery bypass graft with chest incision only (eg, use of internal mammary artery for bypass graft); ENT, ear, nose, and throat.

Table 6. Percentiles of the distribution of SSI rates,^∗ by operative procedure and risk index category,^† Surgical Patient component, January 1992 through June 2004

CBGB, Coronary artery bypass graft with chest and donor site incisions (eg, femoral or radial artery harvested as donor vessel for bypass graft); CBGC, coronary artery bypass graft with chest incision only (eg, use of internal mammary artery for bypass graft).

Table 7. SSI rates,^∗ by selected operative procedure and modified risk index category incorporating laparoscope use,^† Surgical Patient component, January 1992 through June 2004

Table 8. SSI rates^∗ following coronary artery bypass graft (CBGB) operation, by risk index category and specific site, Surgical Patient component, January 1992 through June 2004

Denominators for the risk categories are as follows: Category 0=2718; Category 1=380,340; Category 2=82,535; Category 3=246.

Table 9. Pooled means and percentiles of the distribution of antimicrobial usage rates (defined daily dose^∗ rates^†), by non-ICU inpatient areas and various types of ICU, ICARE/AUR, January 1998 through June 2004

Non-ICU Inpatient Areas (n=74)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	759,866	60.9	9.2	16.7	28.9	63.8	96.5
Ampicillin group	1,899,047	152.1	83.2	111.1	141.7	186.3	266.9
Antipseudomonal penicillins	251,036	20.1	3.1	8.1	16.4	29.0	42.9
Antistaphylococcal penicillins	245,777	19.7	2.9	5.1	12.5	24.2	35.8
First-generation cephalosporins	982,573	78.7	43.9	57.4	76.1	106.6	125.1
Second-generation cephalosporins	368,970	29.6	10.3	16.5	25.3	41.5	54.9
Third-generation cephalosporins	793,340	63.5	21.9	32.2	53.6	79.5	92.5
Carbapenem group	85,779	6.9	0.4	1.8	4.7	9.4	17.1
Aztreonam	34,078	2.7	0.1	0.7	1.8	4.3	6.4
Fluoroquinolones	1,166,836	93.5	37.9	57.9	91.7	130.3	202.2
Trimethoprim/sulfamethoxazole	595,248	47.7	5.3	14.8	24.5	39.2	106.3
Vancomycin (oral)	38,279	3.1	0.1	0.5	1.4	2.5	4.2
Vancomycin (parenteral)	415,887	33.3	13.1	17.1	24.6	41.0	65.7

Coronary Care Unit (n=32)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	4296	30.8	0.0	0.4	7.2	41.7	106.4
Ampicillin group	12,356	88.5	8.6	44.8	88.3	172.1	245.9
Antipseudomonal penicillins	4599	32.9	0.0	3.3	20.8	42.8	58.6
Antistaphylococcal penicillins	3679	26.3	0.0	3.6	12.0	46.2	68.2
First-generation cephalosporins	6978	50.0	9.0	27.7	36.5	54.4	104.9
Second-generation cephalosporins	4286	30.7	1.5	7.1	19.8	32.5	42.4
Third-generation cephalosporins	12,540	89.8	25.1	32.8	73.5	98.0	143.5
Carbapenem group	1635	11.7	0.0	0.2	6.1	12.1	27.4
Aztreonam	777	5.6	0.0	0.0	2.0	10.8	14.9
Fluoroquinolones	12,390	88.7	11.3	27.3	58.9	112.3	214.4
Trimethoprim/sulfamethoxazole	5585	40.0	0.0	6.0	16.5	43.4	112.8
Vancomycin (oral)	526	3.8	0.0	0.0	0.0	1.3	7.0
Vancomycin (parenteral)	7713	55.2	11.2	19.8	36.9	89.3	105.9

Cardiothoracic ICU (n=21)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	3736	38.4	0.0	0.0	4.8	40.9	83.0
Ampicillin group	7044	72.4	3.3	16.6	58.5	97.6	143.2
Antipseudomonal penicillins	2139	22.0	1.4	6.3	16.1	32.1	45.4
Antistaphylococcal penicillins	2483	25.5	0.0	0.0	6.4	31.0	38.6
First-generation cephalosporins	25,925	266.6	36.5	210.3	258.7	465.4	697.9
Second-generation cephalosporins	8997	92.5	2.7	6.8	22.7	73.4	470.1
Third-generation cephalosporins	8941	91.9	17.8	32.2	61.8	97.0	151.1
Carbapenem group	1663	17.1	0.0	1.6	11.8	18.9	49.4
Aztreonam	740	7.6	0.0	0.5	1.9	5.3	9.2
Fluoroquinolones	8065	82.9	8.6	23.2	65.5	101.4	187.4
Trimethoprim/sulfamethoxazole	1601	16.5	0.0	0.5	8.8	21.8	43.9
Vancomycin (oral)	557	5.7	0.0	0.0	0.0	2.5	10.7
Vancomycin (parenteral)	12,081	124.2	26.0	45.6	97.0	156.9	210.9

Hematology/Oncology/Transplant Wards (n=17)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	3416	27.6	—	—	—	—	—
Ampicillin group	17,578	141.8	—	—	—	—	—
Antipseudomonal penicillins	3,599	29.0	—	—	—	—	—
Antistaphylococcal penicillins	1975	15.9	—	—	—	—	—
First-generation cephalosporins	6017	48.5	—	—	—	—	—
Second-generation cephalosporins	2904	23.4	—	—	—	—	—
Third-generation cephalosporins	27,434	221.3	—	—	—	—	—
Carbapenem group	1863	15.0	—	—	—	—	—
Aztreonam	935	7.5	—	—	—	—	—
Fluoroquinolones	20,690	166.9	—	—	—	—	—
Trimethoprim/sulfamethoxazole	4003	32.3	—	—	—	—	—
Vancomycin (oral)	540	4.4	—	—	—	—	—
Vancomycin (parenteral)	10,172	82.1	—	—	—	—	—

Medical ICU (n=36)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	11,598	55.1	0.0	4.9	39.1	63.0	97.5
Ampicillin group	46,702	222.0	89.4	135.5	181.4	253.0	345.4
Antipseudomonal penicillins	14,887	70.8	13.1	30.6	60.4	104.0	170.5
Antistaphylococcal penicillins	9368	44.5	0.0	3.5	25.1	43.6	84.9
First-generation cephalosporins	7456	35.4	10.6	19.5	30.7	39.5	70.3
Second-generation cephalosporins	5986	28.5	1.2	7.0	21.7	47.9	67.1
Third-generation cephalosporins	53,488	254.2	58.2	88.8	140.2	199.3	317.3
Carbapenem group	7889	37.5	0.0	8.0	23.2	37.2	98.3
Aztreonam	1995	9.5	0.0	1.5	6.1	11.8	17.7
Fluoroquinolones	35,393	168.2	39.3	82.5	134.0	184.4	307.7
Trimethoprim/sulfamethoxazole	22,058	104.8	0.0	21.6	40.5	91.7	185.3
Vancomycin (oral)	366	1.7	0.0	0.0	0.3	1.8	6.7
Vancomycin (parenteral)	27,921	132.7	42.9	56.9	79.0	156.4	222.1

Medical-surgical ICU (n=61)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	21,837	46.5	0.0	2.3	13.6	38.7	113.4
Ampicillin group	94,566	201.4	33.1	79.1	185.0	300.8	376.9
Antipseudomonal penicillins	35,471	75.5	18.2	37.2	61.7	95.4	115.5
Antistaphylococcal penicillins	12,079	25.7	1.4	4.8	13.8	29.3	49.0
First-generation cephalosporins	48,262	102.8	23.9	53.5	76.7	126.6	209.2
Second-generation cephalosporins	16,107	34.3	2.6	6.4	19.0	42.5	91.7
Third-generation cephalosporins	67,688	144.1	61.2	80.4	116.4	163.4	200.6
Carbapenem group	17,727	37.8	3.4	8.2	26.8	47.0	62.9
Aztreonam	4785	10.2	0.0	1.9	6.2	14.0	23.9
Fluoroquinolones	96,695	205.9	55.4	92.8	167.5	301.2	360.3
Trimethoprim/sulfamethoxazole	31,448	67.0	0.0	11.5	24.2	68.6	203.4
Vancomycin (oral)	2868	6.1	0.0	0.0	2.4	5.9	9.3
Vancomycin (parenteral)	40,303	85.8	33.1	53.2	66.7	122.9	143.0

Neurosurgical ICU (n=11)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	3294	55.6	—	—	—	—	—
Ampicillin group	6892	116.3	—	—	—	—	—
Antipseudomonal penicillins	2669	45.0	—	—	—	—	—
Antistaphylococcal penicillins	4296	72.5	—	—	—	—	—
First-generation cephalosporins	6949	117.2	—	—	—	—	—
Second-generation cephalosporins	1157	19.5	—	—	—	—	—
Third-generation cephalosporins	7339	123.8	—	—	—	—	—
Carbapenem group	1821	30.7	—	—	—	—	—
Aztreonam	82	1.4	—	—	—	—	—
Fluoroquinolones	5754	97.1	—	—	—	—	—
Trimethoprim/sulfamethoxazole	3835	64.7	—	—	—	—	—
Vancomycin (oral)	74	1.2	—	—	—	—	—
Vancomycin (parenteral)	5923	99.9	—	—	—	—	—

Surgical ICU (n=37)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	17,167	56.3	0.0	8.1	34.7	71.1	109.8
Ampicillin group	63,393	207.8	43.0	100.5	222.5	305.7	445.1
Antipseudomonal penicillins	16,711	54.8	10.1	31.0	49.4	80.7	102.2
Antistaphylococcal penicillins	9107	29.9	0.7	2.9	17.9	35.6	88.4
First-generation cephalosporins	54,317	178.1	38.9	101.2	157.0	365.5	498.0
Second-generation cephalosporins	8081	26.5	3.4	12.8	29.4	47.4	69.2
Third-generation cephalosporins	45,082	147.8	34.4	71.3	99.9	116.7	180.7
Carbapenem group	15,383	50.4	1.0	10.3	19.6	54.9	74.6
Aztreonam	1780	5.8	0.4	4.1	7.1	11.5	19.3
Fluoroquinolones	46,268	151.7	52.2	73.5	131.2	211.0	291.1
Trimethoprim/sulfamethoxazole	22,816	74.8	5.3	10.0	23.9	54.8	179.9
Vancomycin (oral)	1272	4.2	0.0	0.0	0.8	3.1	11.3
Vancomycin (parenteral)	48,435	158.8	45.4	65.9	99.1	155.3	196.0

Pediatric ICU (n=16)			Percentile
Antimicrobial agent	No. DDD∗	Pooled mean	10%	25%	50% (median)	75%	90%
Penicillin group	2162	41.6	—	—	—	—	—
Ampicillin group	4818	92.7	—	—	—	—	—
Antipseudomonal penicillins	575	11.1	—	—	—	—	—
Antistaphylococcal penicillins	1829	35.2	—	—	—	—	—
First-generation cephalosporins	2531	48.7	—	—	—	—	—
Second-generation cephalosporins	1690	32.5	—	—	—	—	—
Third-generation cephalosporins	7564	145.6	—	—	—	—	—
Carbapenem group	421	8.1	—	—	—	—	—
Aztreonam	90	1.7	—	—	—	—	—
Fluoroquinolones	668	12.8	—	—	—	—	—
Trimethoprim/sulfamethoxazole	908	17.5	—	—	—	—	—
Vancomycin (oral)	160	3.1	—	—	—	—	—
Vancomycin (parenteral)	3329	64.1	—	—	—	—	—

Table 10. Pooled means and percentiles of the distribution of antimicrobial resistance rates^∗, by all ICUs combined, non-ICU inpatient units and by outpatients, ICARE/AUR, January 1998 through June 2004

MRSA, Methicillin-resistant Staphylococcus aureus; CNS, coagulase-negative staphylococci; Cef3, ceftazidime, cefotaxime, or ceftriaxone; Quinolone, ciprofloxacin, ofloxacin, or levofloxacin; Carbapenem, imipenem or meropenem.

Table 1, Table 2 from the ICU component update previously published device-associated rates and device utilization (DU) ratios by type of ICU.^1., ^2. As noted above, data from a shorter, more recent time period is presented which differs from previous reports. In general, the device-associated urinary tract and bloodstream infection rates are slightly lower than before. In these tables, the percentile distributions that display the infection rates and DU ratios require data from at least 20 different units. Each of the analyses of ICU data excluded rates or DU ratios for units that did not report at least 50 device-days or patient-days. Because of this, the number of units contributing data in the tables is not exactly the same.

The number of units reporting data from burn and respiratory ICUs is not adequate to provide distributions of infection rates and DU ratios. The data for combined medical/surgical ICUs are split into 2 groups by type of hospital: “major teaching” and “all others.” Major teaching status is defined as a hospital that is an important part of the teaching program of a medical school and a major unit in the clinical clerkship program. The combined medical/surgical ICUs from major teaching hospitals had significantly higher infection rates and DU ratios than combined medical/surgical ICUs from all of the other hospitals. Teaching affiliation was not an important factor for any other type of ICU.

For the ICU component, device-days consist of the total number of ventilator-days, central line-days, and urinary catheter-days. The DU of an ICU is one measure of the unit's invasive practices that constitutes an extrinsic risk factor for nosocomial infection.² As such, DU may also serve as a marker for severity of illness of patients in the unit, that is, patients' intrinsic susceptibility to infection.

Site distributions of infections for coronary care, medical, pediatric, and combined medical-surgical ICUs have been published elsewhere.^10., ^11., ^12., ^13.

Figure 1 shows the rates of antimicrobial resistance among selected pathogens identified from patients in the ICU with nosocomial infections. For each antimicrobial/pathogen pair, the pooled mean rate of resistance for January through December 2003 is displayed. Next to or overlapping this point is the average rate of resistance (±1 SD) over the previous 5-year period (shaded bars). The number of isolates tested from January through December 2003 and the percentage increase in the resistance rate during 2003 compared with the previous 5 years are shown in the 2 columns to the right of the graph. The continuing increase in antimicrobial resistance in U.S. hospitals remains a concern. Of note, the proportion of Staphylococcus aureus isolates that were resistant to methicillin, oxacillin, or nafcillin continues to rise and is nearly 60%, and there has been a nearly 50% increase in nonsusceptible Klebsiella pneumoniae isolates to 3rd generation cephalosporins between 2002 and 2003. However, the rate of increase has diminished for several pathogens, including vancomycin-resistant Enterococcus, which was reported as +31% in 2000 compared to +12% in 2003.¹⁴ Although these data are limited to patients in ICUs, they are not otherwise risk-adjusted and comparisons of these rates between hospitals should be made with caution.

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• Fig 1. 

  Selected antimicrobial-resistant pathogens associated with nosocomial infections in ICU patients, comparison of resistance rates from January through December 2003 with 1998 through 2002, NNIS System. CNS, Coagulase-negative staphylococci; 3rd Ceph, resistance to 3rd generation cephalosporins (either ceftriaxone, cefotaxime, or ceftazidime); Quinolone, resistance to either ciprofoxacin or ofloxacin. ^∗Percent (%) increase in resistance rate of current year (January-December 2003) compared with mean rate of resistance over previous 5 years (1998-2002): [(2003 rate – previous 5-year mean rate)/previous 5-year mean rate] × 100. ^∗∗“Resistance” for E coli or K pneumoniae is the rate of nonsusceptibility of these organisms to either 3rd Ceph group or aztreonam.

Table 3, Table 4 from the HRN component update the previously published, device-associated rates and DU ratios in each of 4 birth weight categories.^1., ^3. For the HRN component, device-days consist of the total number of ventilator-days and umbilical catheter- or central line-days. Each of the analyses of HRN data excluded rates or DU ratios for units that did not report at least 50 device-days or patient-days. Because of this, the number of units contributing data in the tables is not exactly the same. As for the ICU component, there were sufficient data to limit the analysis to the period January 2002 through June 2004. Although the percentile distribution of the rates is provided, for most birth-weight categories the number of pneumonias and ventilator-days is still relatively small and the data should be considered provisional. Percent distributions of infections by major site of nosocomial infection and pathogens by major site, and other HRN analyses, have been published.¹⁵

Table 5, Table 6, Table 7, Table 8 from the surgical patient component update previously published rates.^1., ^4. Table 5 displays SSI rates by operative procedure and NNIS risk index category. When the SSI rates for adjacent risk categories for a particular operation were not statistically different, they were combined into a single risk category. For example, because the SSI rates for cardiac surgery with 2 or 3 risk factors were similar, the data were combined into a new category 2,3. Thus, the number of risk index categories in the tables will differ depending upon the operation. For small bowel and organ transplant operations, rates for risk categories 2 and 3 are now reported separately. For digestive tract operations, rates for risk categories 0 and 1 are now reported separately. However, for 3 other operations, fewer risk categories are reported, ie, for appendectomy and gastric operations, categories 2 and 3 are combined, and for colon operations, categories M and 0 are combined. Further, the duration cut point for liver/pancreas operations increased from 4 to 5 hours, and for other eye operations, it increased from 2 to 3 hours.

For a hospital to be represented in Table 6, it must have reported sufficient data, that is, at least 20 operations in a given risk index category for the procedure. Note that the percentile distributions are not available for every operative procedure and risk index category because percentile distributions of the procedure-specific and risk-index-specific rates required sufficient data from at least 20 hospitals.

Laparoscopes and endoscopes are being used with increasing frequency to perform operations. Table 7 lists 4 operations in which the use of a laparoscope has been incorporated into the SSI risk index. When other risk factors were controlled, cholecystectomy, colon operation, gastric operation, and appendectomy had lower SSI rates when a scope was used. However, there were some differences among these operations. For cholecystectomy and colon operations, the influence of scope use was captured by subtracting 1 from the number of risk factors (ASA score ≥3; duration of operation >75th percentile; or contaminated or dirty wound class) present whenever the procedure was done laparoscopically. “M” indicates minus 1 (−1) in the modified risk category, where no risk factors were present and the procedure was performed with a laparoscope (ie, 0 − 1=−1). For colon operations, in contrast to the previously published report,¹ there is now no significant difference in the rates between risk category M and 0 and so is displayed as a combined M,0 rate in Table 7. For appendectomy and gastric operation, the use of a scope was only important if the patient had no other risk factors. Therefore, we split the index value of 0 risk factors into 0-No and 0-Yes. The percentile distributions of the 4 operative procedures with modified SSI risk index categories have not been developed at this time.

Table 8 displays SSI rates by specific site after coronary artery bypass graft operations in which incisions are made at both the chest and the donor vessel harvest sites.

The data in Table 9, Table 10 are from Phase 3 (January 1998 through November 1999) of the Intensive Care Antimicrobial Resistance Epidemiology (ICARE) Project and the NNIS Antimicrobial Use and Resistance (AUR) component (December 1999 through June 2004) and update previously published reports.^1., ^16., ^17. For the purpose of analysis, grams of antimicrobial agents were converted into number of defined daily doses used each month in each hospital area. A defined daily dose is the average daily dose in grams of a specific antimicrobial agent given to an average adult patient (Appendix A).^18., ^19. Note that unless otherwise indicated, we used the 2004 WHO DDD values,¹⁹ which is different from previous reports. Table 9 shows use of selected oral and parenteral antimicrobial agents in defined daily doses. Antimicrobial use was stratified by route of administration and hospital area. Because outpatient antimicrobial use could not be estimated reliably from hospital pharmacy records, data on outpatient antimicrobial use were not collected. Antimicrobial agents with similar spectrum or clinical indications were grouped and shown in Appendix A. On the basis of detailed analysis, antimicrobial usage rates were found to vary by type of ICU, so usage rates and percentiles are shown for each type of ICU for which there were at least 20 units reporting data. The number of burn and respiratory ICUs reporting usage data is insufficient to include in the table. The number of neurosurgical and pediatric ICUs and hematology/oncology/transplant wards is insufficient to provide percentile distributions; only pooled mean usage rates are displayed. Table 10 shows ICARE/AUR resistance data for selected antimicrobial-resistant bacteria on the basis of reported antimicrobial susceptibility test results on all non-duplicate clinical isolates processed by the laboratory during each study month. A duplicate isolate was defined as an isolate of the same species of bacteria with the same antimicrobial susceptibility pattern in the same patient in the same month, regardless of the site of isolation. All isolates, whether responsible for hospital-acquired or community-acquired infection or for colonization, were reported to ICARE/AUR by participating hospitals. Hospitals used National Committee for Clinical Laboratory Standards interpretive standards for minimum inhibitory concentration, or zone diameter testing standards to report numbers of susceptible, intermediate, or resistant organisms. A minimum of 10 isolates must be tested in a hospital area for resistance rates to be calculated for that area. Resistance data have been combined for all ICU types because detailed analysis demonstrated that, in general, resistance rates (percent prevalence) did not differ by type of ICU. Also, these data show that for most antimicrobial-resistant bacteria, resistance rates are highest in the ICU areas, followed by non-ICU inpatient areas, with lowest rates in the outpatient areas.

If you would like to compare your hospital's rates and ratios with those in this report, you must first collect information from your hospital in accordance with the methods described for the NNIS System.^5., ^6., ^7. You should also refer to Appendices B and C for further instructions. Appendix B discusses the calculation of infection rates and DU ratios for the ICU or HRN surveillance components. Appendix C gives a step-by-step method for interpretation of percentiles of infection rates or DU ratios. A high rate or ratio (>90th percentile) does not necessarily define a problem; it only suggests an area for further investigation. Similarly, a low rate or ratio (<10th percentile) may be the result of inadequate infection detection.

Hospitals should use these data to guide local improvement efforts aimed at reducing infection rates as much as possible.

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Appendix A. Defined daily dose (DDD) of antimicrobial agents, by class and group 

DDD for those agents marked with an asterisk (^∗) are adapted from Amsden GW, Schentag JJ. Tables of antimicrobial agent pharmacology. In: Mandell GL, Bennett JE, Dolin R, editors. Principles and practice of infectious diseases. 4th ed. New York: Churchill Livingstone; 1995. p. 492-528. All other DDD are from: WHO Collaborating Centre for Drug Statistics Methodology. Anatomical Therapeutic Chemical (ATC) classification index with defined daily doses (DDD). 2004. Available from: http://www.whocc.no/atcddd/.

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Appendix B 

How to calculate a device-associated infection rate and device utilization ratio with ICU and HRN component data 

Calculation of device-associated infection rate

Step 4:Determine the number of device-days which is used as the denominator of the rate. Device-days are the total number of days of exposure to the device (central line, ventilator, or urinary catheter) by all of the patients in the selected population during the selected time period.Example: Five patients on the first day of the month had one or more central lines in place: 5 on day 2; 2 on day 3; 5 on day 4; 3 on day 5; 4 on day 6; and 4 on day 7. Adding the number of patients with central lines on days 1 through 7, we would have 5+5+2+5+3+4+4=28 central line-days for the first week. If we continued for the entire month, the number of central line-days for the month is simply the sum of the daily counts.

Step 5:Calculate the device-associated infection rate (per 1000 device-days) using the following formula:

Example:

Calculation of DU ratio

Steps 1,2,4:Same as that for device-associated infection rates, plus determine the number of patient-days which is used as the denominator of the DU ratio. Patient-days are the total number of days that patients are in the ICU (or HRN) during the selected time period.Example: Ten patients were in the unit on the first day of the month; 12 on day 2; 11 on day 3; 13 on day 4; 10 on day 5; 6 on day 6; and 10 on day 7; and so on. If we counted the patients in the unit from days 1 through 7, we would add 10+12+11+13+10+6+10 for a total of 72 patient-days for the first week of the month. If we continued for the entire month, the number of patient-days for the month is simply the sum of the daily counts.

Step 5:Calculate the DU ratio with the following formula:

With the number of device-days and patient-days from the examples above, DU=28/72=0.39 or 39% of patient-days were also central line-days for the first week of the month.

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Appendix C 

Interpretation of percentiles of infection rates or device utilization ratios 

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Appendix D 

CDC NNIS PERSONNEL 

Denise Cardo, MD

Director, Division of Healthcare Quality Promotion (DHQP), National Center for Infectious Diseases

Teresa Horan, MPH

NNIS Coordinator, Healthcare Outcomes Branch (HOB), DHQP

Mary Andrus, BA, RN, CIC

Nurse Epidemiologist, HOB

Margaret Dembinski, BS

MPH Student, HOB

Jonathan Edwards, MS

Mathematical Statistician, HOB

Gloria Peavy

Computer Technical Support, HOB

James Tolson, BS

Information Technology Specialist, HOB

Debra Wagner, BA

MPH Student, HOB

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