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Background and Approach
Carbapenem-Resistant Organisms (CROs) are bacteria resistant to the carbapenem class of antibiotics, which are the
last line treatment for bacterial infections. Some CROs are also Carbapenemase-Producing Organisms (CPOs), which
facilitate resistance by encoding enzymes that break down Carbapenems. These organisms have been identified as ur-
gent health threats. Since 2017 Alameda County Public Health Department (ACPHD) has required reporting of Car-
bapenem-Resistant Klebsiella spp, Enterobacter spp, and Escherichia coli, and isolate submissions to the Public Health
Lab. CROs of other species are encouraged to be reported and isolates submitted. The Health Officer Order (HOO) pre-
cedes State reporting mandates which do not include isolate submission.
ACPHD works with facilities experiencing multidrug-resistant organism (MDRO) outbreaks to limit spread and provide
education regarding prevention and control. Key strategies include root cause analyses using risk-based epidemiology
and acquiring genomic data to inform investigations; closure of affected units pending review and implementation of
mitigation and prevention measures; admission screenings and improved resident cohorting strategies; and reinforcing
interfacility communication as required by the HOO.
Carbapenem-resistant Organisms in
Alameda County, 2023
Provider Recommendations:
• Contact ACPHD if CRO transmission is suspected or if
you need infection prevention and control guidance
• Fill out the interfacility-transfer form when transferring
patients
• Perform Carbapenemase testing on Carbapenem-
Resistant isolates and submit isolates to the public
health lab as mandated
• Screen high-risk patients (admitted from long-term
acute care hospitals, ventilator-equipped SNFs, out-
break facilities, patients with healthcare exposure
abroad, epidemiologically linked to a case) on admission
• Do not re-screen patients with prior CPO detection; im-
plement appropriate infection control measures based
on known history of CPO colonization/infection
Carbapenem-Resistant Organism Cases and
Case–Patients
In 2023 there were 344 CRO cases reported among
311 patients, less than the 380 cases reported in
2022. From January to December 2023 there was
no overall increase or decrease in cases (Figure 1).
The majority of case-patients were over 60 years
old (68%), and male (58%, Table 1). Of patients with
known race and ethnicity, over half were White or
Asian (57%). One-fifth of case-patients were resi-
dents of other counties but were identified in Ala-
meda County facilities, 75% in long-term care facil-
ities (LTCFs).
Figure 1. Carbapenem-Resistant Organism Case Counts by
Month, 2023
Case Clinical and Epidemiologic Data
Of the 344 CRO cases in 2023, 110 (32%) were Car-
bapenemase-producing (Table 2), the same percent
as 2022. Most Carbapenem-Resistant Acinetobacter
baumannii (CRAB) cases (72%) were Carbapenemase-
producing, while most Carbapenem-Resistant Pseu-
domonas aeruginosa (CRPA) cases were not (85%).
Fifty percent of cases (172) occurred among LTCF
residents or patients with a history of long-term care.
The most commonly associated risk factors for CROs
were previous healthcare admission (82%), indwelling
device (73%), and totally dependent on others for dai-
ly activities (71%); 19% of interviewed patients had
international travel prior to testing positive for a CRO,
and of those, 64% received care while travelling.
1100 San Leandro Blvd,
San Leandro, CA 94577
Phone: 510-267-3250
For questions or additional information, contact:
Alameda County Public Health Department
Acute Communicable Diseases Section
Carbapenem-Resistant Organisms, 2023 Page 2
Website: https://acphd.org/communicable-
disease/disease-reporting-and-control/
Last updated June 18th, 2025
Isolates
533 isolates were collected for the 344 cases. Of those,
392 (74%) were tested for at least one CP gene (Table
3). The most commonly identified genes were NDM and
KPC (in 16% and 10% of isolates tested, respectively).
The majority of KPC (89%), VIM (80%), and OXA-237
(78%) genes were identified among case-patients cur-
rently or with a history of residing in LTCFs. The majority
of OXA-48 (75%) and NDM (65%) genes were identified
among cases with no LTCF history.
Table 1. Demographic Characteristics of
Carbapenem-Resistant Organism Case-Patients, 2023
Demographic N = 3111
5-Year Case
Rate per
100,000
Age Group
30 or younger 14 (4.5%) 2.3
31-40 15 (4.8%) 6.6
41-50 25 (8.0%) 12.1
51-60 45 (14%) 22.4
61-70 77 (25%) 47.0
71-80 75 (24%) 80.2
81+ 60 (19%) 126.9
Gender
Female 132 (42%) 16.8
Male 179 (58%) 23.6
Race/Ethnicity
African American/Black 38 (12%) 25.1
Asian 50 (16%) 9.9
Hispanic/Latino/a/x 29 (9.3%) 8.2
Pacific Islander, Native
American, or Multirace 7 (2.3%) 8.6
White 73 (23%) 16.2
Other 20 (6.4%) —
Unknown 94 (30%) —
County Residence
Alameda 251 (81%) 16.25
Other 60 (19%) —
1n (%)
Organism
CRAB CRE* CRPA
Other
CRE/
CRO
Total
Carbapenemase-
Producing
31
(72%)
65
(45%)
11
(8.3%)
3
(14%)
110
(32%)
non-
Carbapenemase-
Producing
6
(14%)
73
(50%)
113
(85%)
13
(59%)
205
(60%)
Not Tested 6
(14%)
8
(5.5%)
9
(6.8%)
6
(27%)
29
(8.4%)
Total 43 146 133 22 344
Table 2. Carbapenemase Status by Organism Group,
2023
Gene CRAB
N = 601
CRE
N = 2121
CRPA
N = 2331
Other
CRE/
CRO
N = 281
Overall
N = 5331
KPC 0/44
(0%)
34/143
(24%)
3/180
(1.7%)
1/15
(6.7%)
38/382
(9.9%)
IMI 0/44
(0%)
0/140
(0%)
0/180
(0%)
0/15
(0%)
0/379
(0%)
VIM 0/44
(0%)
0/140
(0%)
5/182
(2.7%)
0/15
(0%)
5/381
(1.3%)
OXA-48 0/41
(0%)
16/143
(11%)
4/180
(2.2%)
0/15
(0%)
20/379
(5.3%)
NDM 22/45
(49%)
36/143
(25%)
3/180
(1.7%)
1/15
(6.7%)
62/383
(16%)
OXA-181 0/33
(0%)
2/116
(1.7%)
0/162
(0%)
0/13
(0%)
2/324
(0.6%)
OXA-237 17/39
(44%)
0/116
(0%)
1/162
(0.6%)
0/13
(0%)
18/330
(5.5%)
OXA-24/40 1/38
(2.6%)
0/116
(0%)
0/162
(0%)
0/13
(0%)
1/329
(0.3%)
OXA-23 4/39
(10%)
0/116
(0%)
0/162
(0%)
0/13
(0%)
4/330
(1.2%)
GES 0/33
(0%)
0/116
(0%)
0/162
(0%)
0/13
(0%)
0/324
(0%)
Not Tested
for any
genes
14/60
(23%)
63/212
(30%)
51/233
(22%)
13/28
(46%)
141/533
(26%)
1Denominator for each cell indicates the number of isolates tested
for each gene, percent is by cell
*CRE includes reportable CREs—Escherichia coli, Klebsiella spp,
and Enterobacter spp.
Abbreviations: CRAB: Carbapenem-Resistant Acinetobacter bau-
mannii, CRE: Carbapenem-Resistant Enterobacterales, CRPA:
Carbapenem-Resistant Pseudomonas aeruginosa, CRO: Car-
bapenem-Resistant organism
Summary
In 2023, 344 cases of CROs were reported, a 9.5% de-
crease from the previous year. There was no overall trend
of CRO incidence in 2023. About 1/3rd of the cases were
CPOs. Case rates were highest among the elderly popula-
tion and half of cases were among patients currently or
with a history of residing in LTCFs. ACPHD continues to
work with facilities to encourage infection control and pre-
vent ongoing transmission.
Table 3. Genes Identified by Organism Type, 2023