This study will analyze gene expression data (HostDx Sepsis test) from blood samples collected from participants with suspected infections. The primary endpoint of the study is to prospectively validate the HostDx Sepsis test for infections. As a secondary endpoint the correlation of participant prognosis and gene expression results in the HostDx Sepsis test will be validated. Participants presenting to the emergency departments of enrolling sites with a suspected infection and 1 vital signs OR suspected sepsis and 2 vital sign changes as stated in the protocol are meeting enrollment criteria

Subjects presenting to the emergency department with a suspected acute infection will be eligible. Suspected infections may be of a) respiratory, b) urinary, c) intra-abdominal, or d) skin & soft tissue etiology. Subjects with suspected sepsis of any cause will also be eligible.

Blood sample collections: Clinical study staff or the treating physician will obtain patient consent and collect two PAXgene RNA tubes of whole blood by venipuncture. The blood samples will be stored at room temperature overnight prior to being frozen at -80C for long-term storage. Samples will be shipped to the sponsor for testing using the HostDx Sepsis test. An additional tube of blood obtained via venipuncture and stored for shipment to a centralized testing laboratory, where it will be tested for C-reactive protein and procalcitonin. This will be done for all participants, even if they had these tests ordered locally as SOC.

In participants with suspected respiratory tract infections a nasopharyngeal swab will be collected as intervention and sent to the reference laboratory. The sample will be processed in a respiratory pathogen panel (regardless of whether the participants had or had not provided a nasopharyngeal swab for local testing with a respiratory panel as SOC).

Results obtained from microbiological testing of the following additional samples will be recorded if testing had been performed locally as SOC:

1. Suspected urinary tract infection: Urine sample for culture.
2. Suspected skin & soft tissue infection: Swab from wound or abscess drainage, or other sample, for culture.
3. Suspected intra-abdominal infection or abscesses (e.g. appendicitis, diverticulitis, cholecystitis): Swab, biopsy or other sample types for culture
4. Suspected sepsis of any cause: blood cultures (at least 1 set following local guidelines).
5. Suspected respiratory tract infection: sputum culture and/or throat culture.

Inclusion Criteria:

1. Age > 18 year

2. Suspected Suspected acute infection (respiratory, urinary, abdominal, skin & soft-tissue), and at least one of the symptoms OR, Suspected sepsis of any cause as defined by a blood culture order by the treating physician, and at least two of the symptoms:

   • Heart rate: >90 beats/ minute
   • Temperature: >38 C or <36C
   • Respiratory Rate: >20 breaths / minutes or PaO2 of <60 mmHg or SpO2 <90%
   • Systolic blood pressure: <100 mmHg
   • Altered mental status: Per clinical exam

3. Able to provide informed consent, or consent by legally authorized representative.

4. Subjects in the healthy control group will be eligible if they are i) >18 years of age, ii) able to provide informed consent, iii) in their normal state of health, and iv) do not meet inclusion criteria above

Exclusion criteria:

1. Treatment with systemic antibiotics, antiviral agents, or antifungal agents within the past 7 days prior to the emergency department study visit. Participants will not be excluded for the use topical antibiotics, antiviral agents, or antifungal agents.
2. Prisoners, mentally disabled, or unable or unwilling to give consent.
3. Previously enrolled in the present clinical trial

Patients presenting to the ED with acute infections or suspected sepsis