Shared Genetic Risk of Celiac Disease, Crohn’s Disease, Ulcerative Colitis, and Collagenous Colitis

E Stahl et al. Gastroenterol 2020; DOI:https://doi.org/10.1053/j.gastro.2020.04.063 Link: Collagenous Colitis Is Associated With HLA Signature and Shares Genetic Risks With Other Immune-Mediated Diseases

“In this largest genetic study of CC to date with histologically confirmed diagnosis, we strongly implicated the HLA locus and proposed potential non-HLA mechanisms in disease pathogenesis. We also detected a shared genetic risk between CC, celiac disease, CD, and UC.”

 

IBD Update -September 2020

EM Kim et al. Inflamm Bowel Dis 2020; 26: 1232-38. Mucosal Eosinophilia Is an Independent Predictor of Vedolizumab Efficacy in Inflammatory Bowel Diseases n=65 patients. In IBD cohort, colonic eosinophilia (340 +/- 156 vs 236 +/- 124) was associated with clinical non-response to vedolizumab (as was prior anti-TNF treatment). In those with ulcerative colitis, mean eosinophil count was 438 in nonresponders compared to 299 in responders. In those with Crohn’s disease, colonic biopsies showed a non-significant increase in eosinophil count in non-responders compared to responders: 352 vs. 232.

MA Sofia et al. Inflamm Bowel Dis 2020; 26: 1251-9. Poor Sleep Quality in Crohn’s Disease Is Associated With Disease Activity and Risk for Hospitalization or Surgery

  • Ninety-two CD and 82 control subjects
  • Crohn’s disease subjects with Pittsburgh Sleep Quality Index (PSQI) >5 more often had inflammatory phenotypes and reported increased benzodiazepine and psychiatric medication use. Crohn’s disease subjects with PSQI >5 also reported more night awakenings due to pain and bathroom use.
  • The PSQI correlated with HBI
  • PSQI >8 was predictive of surgery or hospitalization (hazards ratio 5.37; 95% confidence interval, 1.39-27.54).

My take: This study indicates that poor sleep is a marker for increased adverse outcomes/disease activity.  It may be that sleep disturbance is due to increased disease activity or this may be a bidirectional issue in which poor sleep triggers more disease activity as well.

A Ricciuto et al. Clin Gastroenterol Hepatol 2020; 18: 1509-1517. Primary Sclerosing Cholangitis in Children With Inflammatory Bowel Diseases Is Associated With Milder Clinical Activity But More Frequent Subclinical Inflammation and Growth Impairment

This retrospective study provides additional information on the observation that children with PSC often have subclinical disease; it is similar to a prospective study by the same group in 2018 (n=37):  (prior blog post: Active Colitis More Likely in Children in Clinical Remission Who Have IBD and PSC) Key finding: Higher proportions of children with PSC-IBD had backwash ileitis, pancolitis, and rectal sparing, and more severe right-sided disease, than controls (P < .05). Conclusions: “Despite the mild clinical activity of IBD in patients with PSC, lack of symptoms does not always indicate lack of mucosal inflammation. Children with PSC-IBD have greater growth impairments compared with children with ulcerative colitis or IBD-unclassified.”

Can Microscopic Colitis Lead to Crohn’s Disease or Ulcerative Colitis?


A recent prospective cohort “ESPRESSO” study (H Khalili et al. Gastroenterol 2020; 158: 1574-83) from 1990-2017 examined the risk of incident inflammatory bowel disease (IBD) in subjects with microscopic colitis, n=13,957 (& each matched with 5 controls). ESPRESSO = Epidemiology Strengthened by histoPathology Reports in Sweden.

Key findings:

  • In the microscopic colitis group, there were 323 incident cases of ulcerative colitis (UC) and 108 cases of Crohn’s disease (CD)
  • Mean times to diagnosis were 3.2 years for UC and 3.3 years for CD
  • Microscopic colitis was associated with an aHR of 12.6 for CD and 17.3 fo rUC
  • The absolute excess risk compared to matched control over a 10-year period were 2.6% for UC and 0.9% for CD

My take: Individuals with microscopic colitis are at increased risk of developing UC and CD.

Related blog post/related article:

 

IBD Briefs June 2020

SA Draiweesh et al. Safety of Combination Biologic and Antirejection Therapy Post-Liver Transplantation in Patients with Inflammatory Bowel Disease. Inflamm Bowel Dis 2020; 26: 949-59. In this case series of 19 patients, 14 who had liver transplantation for PSC, there was no increased risk of serious infections among patients receiving biologic therapy in combination with antirejection medications.

A Malian et al. Pedictors [sic] of Perianal Fistula Relapse in Crohn’s Disease. Inflamm Bowel Dis 2020; 26: 926-31. In this retrospective study with 137 patients, fistula relapse rates were not different in patients receiving infliximab or adalimumab (P = 0.66). In patients treated by anti-TNF at inclusion, discontinuation of anti-TNF therapy (odds ratio 3.49, P = 0.04), colonic location (OR 6.25, P = 0.01), and stricturing phenotype (odds ratio 4.39, P = 0.01) were independently associated with fistula relapse in multivariate analysis.

M-H Wang et al. Unique Phenotypic Characteristics and Clinical Course in Patients With Ulcerative Colitis and Primary Sclerosing Cholangitis: A Multicenter US Experience. Inflamm Bowel Dis 2020; 26: 774-81. Among 522 patients with UC, 56 (10.7%) had PSC. Compared with UC alone, patients with UC-PSC were younger (younger than 20 years) at diagnosis (odds ratios [OR], 2.35; adjusted P = 0.02) and had milder UC severity (adjusted P = 0.05), despite having pancolonic involvement (OR, 7.01; adjusted P < 0.001).  In the biologics era (calendar year 2005 to 2015), patients with UC-PSC less commonly received anti-TNF therapy compared with patients with UC (OR, 0.38; adjusted P = 0.009), but their response rates were similar.

B Barberio et al. Matrix Metalloproteinase 3 Predicts Therapeutic Response in Inflammatory Bowel Disease Patients Treated with Infliximab. Inflamm Bowel Dis 2020; 26: 756-62. Retrospectively, 73 IBD patients who had received IFX for at least 1 year were enrolled: 35 patients were responders and 38 were nonresponders at 52 weeks…The MMP3 levels were similar at baseline (19.83 vs 17.92 ng/mL), but at postinduction, patients who failed to respond at 1 year had significantly higher levels than patients who responded (26.09 vs 8.68 ng/mL, P < 0.001); the difference was confirmed at week 52 (29.56 vs 11.48 ng/mL, P < 0.001)…The MMP3 serum determination may represent an early marker of response to infliximab.

 

“No Solid Conclusions” for Alternative/Complementary Therapies for Inflammatory Bowel Disease

In this clinical review (N Chande et al Inflamm Bowel Dis 2020; 26: 843-51) assess evidence from Cochrane reviews of four popular nontraditional treatments for inflammatory bowel disease (IBD):

  • Fecal Microbiota Transplantation (FMT)
  • Nutritional Therapies including Enteral Nutrition (EN)
  • Naltrexone for Crohn’s Disease (CD)
  • Cannabis for IBD

So what does the literature have to say about these treatments:

  • FMT: FMT for mild to moderate ulcerative colitis (UC) increased the proportion of patients achieving clinical remission. “However, the number of included studies was small and the quality of evidence was low.”  Other problems included uncertainty regarding serious adverse events and short duration of followup.
  • “As a result, no solid conclusions [the authors did not indicate this as a pun] can be drawn at this time.”

  • Nutritional Therapies: For remission in CD, “EN may be more effective than corticosteroids in children, although the opposite was true in adults.”
  • “Exclusion diets did not promote clinical remission or reduce clinical relapse in UC”
  • “The overall certainty of evidence in these studies were generally very low, largely due to sparse data.”

  • Naltrexone for Crohn’s Disease (CD): “The paucity of data makes it impossible to draw any firm conclusions about the effectiveness and safety” of low dose naltrexone.

  • Cannabis for IBD: “The risk of adverse events was significantly higher in cannabis-treated patients”…though these events were generally mild (eg. sleepiness, confusion, nausea).
  • “The results of these studies suggest that cannabis is not effective for the treatment of IBD”  This conclusion is limited by the small number of patients in prior studies.  Cannabis may be helpful as an adjunct for some symptoms though this “warrants further study.”

Related blog posts:

 

 

Ionizing Radiation Exposure in Adults with Inflammatory Bowel Disease

From The Onion:


In the largest reported cohort to date, GC Nguyen et al (Inflamm Bowel Dis 2020; 26: 898-906) describe the ionization radiation exposure (IRE) in individuals (≥18 years) with inflammatory bowel disease (IBD).

Methods: N=72,933 with IBD,1994-2016. During 1st 5 yrs after diagnosis, IRE was estimated in a retrospective matched cohort in Ontario.

Key findings:

  • IBD patients were exposed to nearly 6-fold IRE due to abdominal imaging compared to controls: 18.6 mSv vs 2.9 mSv
  • Patients with CD had higher IRE than UC: 26 mSv vs 12 mSv (P<0.001).  CD patients were more likely to have >50 mSv exposure (15.6% vs 6.2%) and >100 mSv 5.0% vs 2.1%
  • Women were less likely to have high IRE compared to males
  • Residents in the poorest neighborhoods were 27% more likely to have IRE >100 mSv.  Socioeconomic status was an independent factor after accounting for comorbidities. The authors speculate that this could be related to increased use of emergency rooms where they may be more likely to receive a CT.
  • The use of CT scan began to decline after 2007…likely explained by the rise of MRE studies.

While strict guidelines on IRE are lacking, the International Commission on Radiological Protection has suggested that occupational exposure (eg. nuclear workers) should be limited to <100 mSv over 5 years and not more than 50 mSv in a single year.

My take: We need to continue efforts to reduce IRE due to concerns about subsequent secondary malignancies. This likely means avoiding CT for non-emergencies and working with our ED colleagues to think carefully about lifetime IRE in IBD patients.

Related blog posts:

Additional references:

  • -AJR 2001; 176: 289-96. Estimated risks of radiation-induced fatal cancer from pediatric CT
  • -Br J Radiol 2012; 85: 523-28.  Justification of CTs -some not needed
  • -AJR 2010; 194: 868-73.  Lower CT radiation doses in pediatric patients.  ‘Image gently’
  • -Arch Intern Med 2009; 169: 2078-86.

From LA Times:


 

Expert Guidance on Inflammatory Bowel Disease (Part 2)

A recent issue of Clinical Gastroenterology and Hepatology focused solely on the clinical features and management of inflammatory bowel disease. Even for those with expertise in IBD, there is a lot of useful information and concise reviews of what is known.

Here are some of my notes from this issue (part 2)

S Danese et al. Clinical Gastroenterol Hepatol: 2020; 18: 1280-90. Positioning Therapies in Ulcerative Colitis

This is a good article but recent AGA publications are probably better –there are some links below. One statement that was interesting: “the safety profile of vedolizumab seems even better than placebo in terms of risk of serious” adverse events. The authors favored infliximab in combination with azathioprine in those needing biologic therapy with moderate-severe UC.

Related blog posts:

S Vermeire et al. Clinical Gastroenterol Hepatol: 2020; 18: 1291-9. How, When, and for Whom Should We Perform Therapeutic Drug Monitoring?

“Although reactive TDM, testing at time of loss of response, is widely accepted in practice, especially for anti–tumor necrosis factor antibodies, there are less data for the other monoclonal antibodies belonging to other classes. Besides reactive testing, there is a movement toward proactively adjusting biologic dosing to prevent loss of response, in keeping with the tight control philosophy of inflammatory bowel disease care.” The authors favor proactive monitoring: “we are now beginning to see with well-powered proactive TDM studies” that proactive monitoring can maximize the benefits of TDM with “the potential to maximize durability of biologics and improve the outcomes of IBD patients.”

Related blog posts:

PS Dulai et al. Clinical Gastroenterol Hepatol: 2020; 18: 1300-8. How Do We Treat Inflammatory Bowel Diseases to Aim For Endoscopic Remission?

The initial part of this article reviews treatment targets -resolution of symptoms and resolution of endoscopic damage. The algorithm provides the authors’ suggested approach:

  • At initiation of therapy, patients should have a full assessment.  In addition to ileocolonoscopy, for patients with CD, the authors recommend cross-sectional imaging.
  • After treatment initiation, the authors recommend biomarker assessment every 3 months.  Mucosal assessment can occur 6-9 months after treatment initiation.
  • For UC, the authors note that fecal calprotectin (FC) “appears to be more stratightforward, and a cutoff of 250 mcg/g can be used reliably across all scenarios to make treatment adjustments.”  Though, they recommend endoscopic confirmation prior to transition to a biologic or small molecule therapy.
  • For CD, the authors suggest making treatment adjustments in those with FC >250 mcg/g and in those with lower values, followup colonoscopy is recommended.
  • The authors note that in the post-operative setting with CD, mucosal inflammation precedes symptomatic activity and “waiting for symptoms to emerge may unnecessary allow for disease progression.”
  • The authors suggest that tighter disease control will reduce disease-related complications, while acknowledging a lack of prospective clinical trials.
  • One thorny issue: :”For CD: it remains unclear what degree of residual mucosal healing is acceptable to impact important outcomes such as CD-related complications, hospitalizations, and surgeries.”

Related blog posts:

M Allocca et al. Clinical Gastroenterol Hepatol: 2020; 18: 1309-23. Use of Cross-Sectional Imaging for Tight Monitoring of Inflammatory Bowel Diseases

“Computed tomography is limited by the use of radiation, while the use of magnetic resonance enterography (MRE) is limited by its cost and access. There is growing interest in bowel ultrasound that represents a cost-effective, noninvasive, and well-tolerated modality in clinical practice, but it is operator dependent… Diffusion-weighted imaging (DWI) is a MR imaging technique that increasingly is used in both IBD and non-IBD conditions and has been shown to be a valuable and accurate tool for assessing and monitoring IBD activity.

L Beaugerie et al. Clinical Gastroenterol Hepatol: 2020; 18: 1324-35. Predicting, Preventing, and Managing Treatment-Related Complications in Patients With Inflammatory Bowel Diseases

The first part of this article reviews potential adverse effects from the medications used for IBD treatment, noting in Table 1 that there are not complications to monitor for with both vedolizumab and ustekinumab.

The article reviews infections, vaccination strategies and issues related to malignancy Some of the recommendations:

  • vaccine against pneumococcus should be given before patients begin immunosuppressive therapy
  • physicians should consider giving patients live vaccines against herpes zoster (in adults) before they begin immunosuppressive therapy or a recombinant vaccine, when available, at any time point during treatment
  • sun protection and skin surveillance from the time of diagnosis are recommended
  • despite concerns about therapy, the authors note that “the extensive use of immunosuppressive therapy leads to a substantial decrease in the incidence of IBD complications, with a globally favorable benefit-risk ratio, which can be optimized further thanks to a good degree of awareness and knowledge of drug complications.”

It is interesting that this article (and the entire issue) does not address mental health concerns related to the diagnosis of IBD.  This likely creates more morbidity and complications than most of the other issues that are discussed.

Above: Why did the picture go to jail? Because it was framed.

Disclaimer: This blog, gutsandgrowth, assumes no responsibility for any use or operation of any method, product, instruction, concept or idea contained in the material herein or for any injury or damage to persons or property (whether products liability, negligence or otherwise) resulting from such use or operation. These blog posts are for educational purposes only. Specific dosing of medications (along with potential adverse effects) should be confirmed by prescribing physician.  Because of rapid advances in the medical sciences, the gutsandgrowth blog cautions that independent verification should be made of diagnosis and drug dosages. The reader is solely responsible for the conduct of any suggested test or procedure.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition.

IBD Updates: Depression and Crohn’s Disease, Blood Tests in Pediatric IBD

LW Gaines et al. Inflamm Bowel Dis 2020; 26: 423-8. In this study with 3307 adults with Crohn’s disease (CD) and baseline demographics, CD activity and an affective-cognitive index of depression, the authors used structural equation models to determine the likelihood of whether depression triggers CD activity or whether CD activity triggers depression.  Key findings: “The hypothesis that an affective-cognitive depression predicts patient-reported exacerbation of CD is 218 times more likely to account for the data than the converse.”   (Depression is likely to increase CD activity rather than be due to CD activity).

JJ Ashton et al. Inflamm Bowel Dis 2020; 26: 469-76. Among 256 patients (dx 2013-17) in Southhampton-PIBD database, there were 151 with CD, 95 with UC and 10 IBD-unclassified.  Key findings:

  • 9% presented with all normal blood tests (tests analyzed if available: CRP, ESR, Albumin, platelets, packed cell volume, wbc, ALT)
  • Normal labs were more common with UC compared to CD: 14.4% vs 5.3%

RC Ungaro et al. AP&T; 2020; DOI: 10.1111/apt.15685.  (Thanks to Ben Gold for this reference).  Systematic review with meta-analysis: efficacy and safety of early biologic treatment in adult and paediatric patients with Crohn’s disease. A total of 18 471 patients were studied, with  a median follow-up of 64 weeks (range 10-416). Meta-analysis found that early use of biologics was associated with higher rates of clinical remission (OR 2.10 [95% CI: 1.69-2.60], n = 2763, P < 0.00001), lower relapse rates (OR 0.31 [95% CI: 0.14-0.68], n = 596, P = 0.003) and higher mucosal healing rates (OR 2.37 [95% CI: 1.78-3.16], n = 994, P < 0.00001) compared with late/conventional management. Conclusions: Early biologic treatment is associated with improved clinical outcomes in both adult and paediatric CD patients, not only in prospective clinical trials but also in real-world settings.

RS Boneh et al. Dietary Therapies Induce Rapid Response and Remission in Pediatric Patients With Active Crohn’s Disease Clin Gastroenterol Hepatol (online April 14, 2020, in press) Thanks to KT Park’s Twitter feed for this reference.

  • Methods: We collected data from the multicenter randomized trial of the CD exclusion diet (CDED). We analyzed data from 73 children with mild to moderate CD (mean age, 14.2±2.7 y) randomly assigned to groups given either exclusive enteral nutrition (EEN, n=34) or the CDED with 50% (partial) enteral nutrition (n=39). Patients were examined at baseline and at weeks 3 and 6 of the diet. Remission was defined as CD activity index scores below 10 and response was defined as a decrease in score of 12.5 points or clinical remission. Inflammation was assessed by measurement of C-reactive protein.
  • Results: At week 3 of the diet, 82% of patients in the CDED group and 85% of patients in the EEN group had a dietary remission (DiRe). Median serum levels of C-reactive protein had decreased from 24 mg/L at baseline to 5.0 mg/L at week 3 (P<.001). Among the 49 patients in remission at week 6, 46 patients (94%) had a DiRe and 81% were in clinical remission by week 3. In multivariable analysis, remission at week 3 increased odds of remission by week 6 (odds ratio, 6.37; 95% CI, 1.6–25; P=.008) whereas poor compliance reduced odds of remission at week 6 (odds ratio, 0.75; 95% CI, 0.012–0.46; P=.006).
  • Conclusions: For pediatric patients with active CD, dietary therapies (CDED and EEN) induce a rapid clinical response (by week 3).

Related blog posts:

Disclaimer: This blog, gutsandgrowth, assumes no responsibility for any use or operation of any method, product, instruction, concept or idea contained in the material herein or for any injury or damage to persons or property (whether products liability, negligence or otherwise) resulting from such use or operation. These blog posts are for educational purposes only. Specific dosing of medications (along with potential adverse effects) should be confirmed by prescribing physician.  Because of rapid advances in the medical sciences, the gutsandgrowth blog cautions that independent verification should be made of diagnosis and drug dosages. The reader is solely responsible for the conduct of any suggested test or procedure.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition

 

AGA Guidelines: Moderate to Severe Ulcerative Colitis

Full Text: JD Feuerstein et al. Gastroenterol 2020; 158: 1450-61. AGA Clinical Practice Guidelines on the Management of Moderate to Severe Ulcerative Colitis

Full Tex PDF: AGA Clinical Practice Guidelines on the Management of Moderate to Severe Ulcerative Colitis

 

Associated articles included the following:

  • Clinical decision support tool (1462-63)
  • PDF: Spotlight (summary -images above) (1464)
  • Technical Review (1465-96)

Key recommendations:

  • 2a. In adult outpatients with moderate to severe UC who are naïve to biologic agents, the AGA suggests using infliximab or vedolizumab rather than adalimumab, for induction of remission. Comment: Patients, particularly those with less severe disease, who place higher value on the convenience of self-administered subcutaneous injection, and a lower value on the relative efficacy of medications, may reasonably chose adalimumab as an alternative
  • 2c. In adult outpatients with moderate to severe UC who have previously been exposed to infliximab, particularly those with primary nonresponse, the AGA suggests using ustekinumab or tofacitinib rather than vedolizumab or adalimumab for induction of remission.
  • 6. In adult outpatients with moderate to severe UC, the AGA suggests early use of biologic agents with or without immunomodulator therapy rather than gradual step up after failure of 5-ASA. Comment: Patients, particularly those with less severe disease, who place higher value on the safety of 5-ASA therapy and lower value on the efficacy of biologic agents or tofacitinib may reasonably chose gradual step therapy with 5-ASA therapy.
  • 10. In hospitalized adult patients with ASUC refractory to intravenous corticosteroids, the AGA suggests using infliximab or cyclosporine

Summary of recommendations:

Related blog posts:

Disclaimer: This blog, gutsandgrowth, assumes no responsibility for any use or operation of any method, product, instruction, concept or idea contained in the material herein or for any injury or damage to persons or property (whether products liability, negligence or otherwise) resulting from such use or operation. These blog posts are for educational purposes only. Specific dosing of medications (along with potential adverse effects) should be confirmed by prescribing physician.  Because of rapid advances in the medical sciences, the gutsandgrowth blog cautions that independent verification should be made of diagnosis and drug dosages. The reader is solely responsible for the conduct of any suggested test or procedure.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition

Ups (mostly) and Downs with IBD Epidemiology

Two articles describe both increasing and decreasing trends in the prevalence of inflammatory bowel disease (IBD).

  • Y Ye et al. Inflamm Bowel Dis 2020; 26: 619-25, editorial 626-27
  • M Torabi et al. Inflamm Bowel Dis 2020; 26: 581-90, editorial 591-92 

The first study by Ye et al provides the familiar message that IBD prevalence has been increasing in pediatrics and adults.  This study examined 2 large claims databases.  The Optum database covered ~18 million annually during the study period (total ~57 million from 2007-2017) and Truven covered ~44 million annually (total ~240 million since 1995)

Key findings:

  • Pediatric IBD prevalence increased by 133% from 2007 to 2016: from 33 per 100,000 to 77 per 100,000. Crohn’s disease (CD) was twice as prevalent as ulcerative colitis (UC) in the pediatric population (46 vs 22)
  • Adult IBD prevalence increased by 123% from 2007 to 2016: from 215 per 100,000 to 478 per 100,000. The prevalence rates of CD and UC were similar in adults: 198 vs 181)
  • The Northeast region had the highest prevalence of IBD, followed by Midwest, South and then West.
  • Based on these prevalence data, there are an estimated 58,000 children (2-17) and 1.2 million adults with IBD in U.S.   Or, 1 in 1299 children and 1 in 209 adults.

Limitations:

  • Diagnosis and data derived from claims database
  • Cases can vary significantly based on how sensitive the definition for IBD is in a given study.  In this study, the authors indicate in supplementary material, that the prevalence rates could be doubled in adults if they chose a more sensitive/less specific case definitions.

The second study by Torabi et al, which utilized the Manitoba Epidemiology Database (n=1.2 million) showed a decrease in IBD incidence.  The authors examined 296 small geographic areas (SGAs) and found that many had persistently high IBD incidence rates.

Key findings:

  • The incidence of IBD decreased from 1990 when it was 23.6 per 100,000 to 16.2 per 100,000 in 2012.
  • In the study period (1990-2012), there were 3114 cases of CD and 3499 cases of UC diagnosed in Manitoba

In the discussion, the authors speculate on the reasons for the decline in IBD incidence in an area with high rates of IBD.  Some of the change may be related to changes in the population mix –more immigrants from areas with lower rates of IBD.  In the editorial, it is noted that a recent systematic review (Lancet 2018; 390: 2769-78) indicated that the “incidence of IBD is stabilizing in Western countries.”

My take: There are a lot kids and adults with IBD.  The preponderance of epidemiology studies point to increasing incidence and prevalence.

Related blog posts:

Rock art during “social distancing”