Point-of-Care Ultrasound by Nonexpert Operators Demonstrates High Sensitivity and Specificity in Detecting Gallstones: Data from the Samoa Typhoid Fever Control Program

Abstract

Approximately 90% of chronic typhoid carriers with persistent Salmonella enterica serovar Typhi (S. Typhi) gallbladder infection have gallstones. In Samoa, where typhoid fever has been endemic for many decades, risk factors predisposing to the development of gallstones are increasing among adults. The Samoa Typhoid Fever Control Program dispatches a "Typhoid Epidemiologic SWAT Team" to perform a household investigation of every blood culture-confirmed case of acute typhoid fever. Investigations include screening household contacts to detect chronic carriers. Following limited training, two nonexpert ultrasound operators performed point-of-care ultrasound (POCUS) on 120 Samoan adults from August to September 2019 to explore the feasibility of POCUS to detect individuals with gallstones during household investigations and community screenings. POCUS scans from 120 Samoan adults in three cohorts (28 food handlers, two typhoid cases and their 18 household contacts, and 72 attendees at an ambulatory clinic) were reviewed by a board-certified radiologist who deemed 96/120 scans (80%) to be interpretable. Compared with the radiologist (gold standard), the nonexpert operators successfully detected 6/7 Samoans with gallstones (85.7% sensitivity) and correctly identified 85/89 without gallstones (95.5% specificity). The proportion (24/120) of uninterpretable scans from this pilot that used minimally trained clinicians (who are neither radiologists nor ultrasound technicians) indicates the need for additional training of POCUS operators. Nevertheless, this pilot feasibility study engenders optimism that in the Samoan setting nonexperts can be trained to use POCUS to diagnose cholelithiasis, thereby helping (along with stool cultures and Vi serology) to identify possible chronic S. Typhi carriers.

Figure 1.

Summary diagram of enrolled participants and subsequent analysis. POCUS = point-of-care ultrasound; HH = household.

Figure 2.

Nonexpert POCUS operator (S.A.H.) performing field examination for gallstones using the Butterfly iQ ultrasound probe. POCUS = point-of-care ultrasound.

Figure 3.

A single, large gallstone identified using the Butterfly iQ ultrasound probe in the course of screening performed by nonexpert POCUS operators. This POCUS image demonstrates the classical ultrasound characteristics of gallstones including a highly reflective echo from the anterior surface of the gallstone and marked posterior acoustic shadowing. With change of the subject’s position, the gallstone also typically changes position, which is readily detected during the POCUS examination. POCUS = point-of-care ultrasound.