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

Seth Hoffman,Linatupu Punimata,Robert Thomsen,Michael Sikorski,Savitra Rambocus,Roy Robins-Browne,Chandler Tuilagi,Myron Levine,Jane Han,Sachin Desai,Take Naseri,Michelle Sialeipata,Glenn Fatupaito,Susana Nimarota-Brown,Siaosi Tupua

doi:10.4269/ajtmh.21-0973

Abstract

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.

Highlights

Typhoid fever is endemic in the island nation of Samoa, in Oceania
In adults recently vaccinated with Vi-conjugate vaccine, Vi serology is unlikely to be useful in screening for chronic carriers
Of the 120 adults in the three cohorts who had point-of-care ultrasound (POCUS) scans performed by the two nonexpert operators, 24 (20%) were adjudicated by the expert radiologist as uninterpretable, leaving 96 interpretable scans

Summary

Introduction

Typhoid fever is endemic in the island nation of Samoa, in Oceania. Approximately 2–4% of untreated acute Salmonella enterica subspecies enterica serovar Typhi Typhi) infections, clinical or subclinical, become “chronic carriers” who excrete for more than 12 months, and typically for decades.[1,2] And 90% of known chronic carriers have gallstones and harbor S. Typhi in their gallbladder.[3,4]. In addition to systemic improvements to water and sanitation infrastructure, a new tool to help control endemic typhoid fever is Vi conjugate vaccine. Chronic carriers can be systematically identified (by stool culture and IgG Vi antibody titer) and treated if the antimicrobial susceptibility of the endemic strain(s) allows.[11,12,13] Of note, in adults recently vaccinated with Vi-conjugate vaccine, Vi serology is unlikely to be useful in screening for chronic carriers

Methods

Results

Conclusion