The overall goals of this project are to evaluate the use of 5-day intensively-delivered Cognitive Processing Therapy to treat PTSD and to determine the associations between the microbiome, salivary cytokines, and the presence of and recovery from PTSD. Specifically, this study is designed to 1) determine whether individual Cognitive Processing Therapy (CPT) delivered twice per day over 5 consecutive days (CPT-5) is tolerable, acceptable, and effective in reducing PTSD symptoms, 2) determine the microbial signatures associated with PTSD, 3) evaluate whether the abundance and composition of microbiota and salivary cytokine levels change over the course of PTSD treatment, and 4) examine whether changes in microbial signatures are associated with changes in cytokine levels.

This project will evaluate the use of 5-day intensively-delivered Cognitive Processing Therapy to treat PTSD and will aim to determine the associations between the microbiome, salivary cytokines, and the presence of and recovery from PTSD. A total of 24 participants who have experienced a criterion A trauma will be recruited. An intake assessment will be used to confirm the fit for the proposed project. Clinical interviewers with a minimum of a Master's degree in Psychology who are not providing the treatment will administer structured diagnostic interviews (CAPS and DIAMOND). If an individual meets criteria for a PTSD diagnosis based on the CAPS they will be eligible for this treatment study.

Study staff will administer brief computerized assessments (e.g. Stroop task), a full self-report assessment battery, and two internet-based dietary assessments to all participants. Study staff will also collect fecal- and oral-derived microbiota and salivary cytokine samples from individuals who opt in to this aspect of the study.

Study Treatment - Intensive Week-Long Cognitive Processing Therapy (CPT):

The individuals in this study will undergo a course of 1-week-long Cognitive Processing Therapy (CPT-5). CPT-5 will be delivered twice per day over the course of five business days. Each 50 minute session will closely follow the CPT protocol and will be conducted by either Dr. Held, other doctoral-level psychologists, postdoctoral fellows, or other Master's level (or higher) clinicians who have received the official two-day CPT training and who are not involved in study assessments. CPT worksheets and homework assignments may be collected and copied for research purposes. Changes in PTSD severity and other relevant symptoms will be assessed before, during, and after the course of CPT using well-validated clinician-administered, self-report, and computerized assessments. Fecal- and oral-derived microbiota as well as salivary cytokines will also be assessed at various pre-treatment, post-treatment, and follow-up time points to determine whether the microbiome and cytokine levels change over the course of CPT. Participants in this study will have the option to opt out of providing these biological samples and still receive CPT-5.

Semi-Structured Interview:

Regardless of whether they completed the course of CPT, participants in the study may be asked to participate in one 20-40 minute semi-structured interview. The interviewer, who is a member of the research team and not the respective participant's study therapist, will ask general questions about the participant's experiences of CPT-5 and gather information about the participant's perceptions of the tolerability, acceptability, and feasibility of the intervention.

Inclusion Criteria:

Individuals are eligible for the study if they:

1. Are 18 years or older
2. Are fluent in English
3. Have experienced a Criterion A traumatic event during their lifetime
4. Have a PTSD diagnosis verified by the Clinician Administered PTSD Scale for DSM-5
5. Are interested in receiving evidence-based treatment (CPT) for PTSD and able to attend 10 therapy sessions over the course of one week (5 days)
6. Are willing and interested to complete self-report measures and clinician-rated assessments at multiple time points over the course of the study

Exclusion Criteria:

Individuals are excluded from the study if:

1. The traumatic event occurred in the past month
2. They are currently suicidal or homicidal, as indicated by a positive screen on the C-SSRS Question 4 or Question 5 at intake.
3. They have a history of psychosis or mania
4. They have not been on a stable dose of medication for at least one month
5. They have dietary patterns not representative of normal populations (e.g., vegetarian, vegan, gluten-free)
6. They made changes to the diet in the past month or are planning to make changes over the course of therapy
7. They have completed an evidence-based PTSD treatment in the past 3 months or are currently receiving an evidence-based PTSD treatment
8. They have mental retardation or significant cognitive impairment that would prevent them from engaging in CPT
9. They have a serious or unstable medical illness or instability for which hospitalization may be likely within the next year
10. They have an active substance use disorder (within the past 3 months)
11. They are involved with current legal actions related to the traumatic event that is anticipated to be targeted during treatment
12. They have a history or presence of an eating disorder
13. They are currently taking or have taken an antibiotic in the past 30 days
14. They are currently taking a corticosteroid
15. They have had part of the digestive tract removed or altered
16. They have had any surgery or procedure within the past 30 days that has required fasting for more than 12 hours or bowel preparation beforehand
17. They are unwilling to provide fecal and saliva samples (applies to trauma-exposed control condition only)

Data were collected from Baseline to 3 months follow up.