Rising Threat of Typhoid Fever
Typhoid fever, once easily managed with antibiotics, is making a comeback. The bacteria Salmonella typhi has developed resistance to nearly all available antibiotics.
Jason Andrews from Stanford University expressed concern, stating, “The rapid emergence and spread of highly-resistant strains of S. typhi is alarming.”
Understanding Typhoid Resistance
Today’s treatments rely on antibiotics working faster than the bacteria can adapt. Unfortunately, whenever medication is improperly used—like when treatment is interrupted or incorrect drugs are given—the risk of developing antimicrobial resistance increases.
Research involving 3,489 samples from India, Pakistan, Nepal, and Bangladesh has shown that resistant strains are replacing the susceptible varieties in just a few years.
Some of these tested samples exhibit three mutations in DNA-gyrase genes, significantly increasing the amount of ciprofloxacin needed to treat infections, effectively removing a standard outpatient option.
As ciprofloxacin became less effective, third-generation cephalosporins took over in the early 2000s. However, a recent survey in Ahmedabad, India, found a notable cluster resistant to ceftriaxone, ampicillin, ciprofloxacin, and trimethoprim-sulfamethoxazole, marking the largest outbreak of ceftriaxone-resistant typhoid identified so far.
The antibiotic azithromycin remains effective, although laboratory monitoring in Pakistan has detected increasing resistance, and U.S. reports this year identified the first azithromycin-resistant cases originating domestically.
Resistance in typhoid is attributed to a single mutation in the AcrB efflux pump, which expels the drug before it can be effective. This mutation has recurred multiple times since 2013, based on genomic tracking.
If azithromycin fails, the next option would be expensive intravenous carbapenems, which may be unavailable in many affected regions, making hospitalization the only viable solution for many patients.
Typhoid Vaccines Available
There are three licensed typhoid vaccines globally, and one conjugate vaccine is safe for infants as young as six months. The WHO advises high-burden countries to introduce this conjugate vaccine in hopes of reducing cases before resistance spreads further.
Pakistan was the first country to include this vaccine in its routine immunization schedule in 2019, and early data indicates a decline in childhood cases in vaccinated areas, providing a cushion for antibiotic development.
Economic forecasts from India suggest that urban vaccination may prevent over a third of typhoid-related deaths in the next decade. The benefits would increase with the rise of resistant strains, as preventing infections also helps avoid costly hospitalizations.
Roots of Antibiotic Resistance
The same travel routes utilized by people also facilitate the movement of pathogens. Genomic studies have traced at least 59 instances of S. typhi moving across continents since 1990, primarily from South Asia.
Once established, local water and sanitation issues allow these strains to thrive. East Africa and Southeast Asia are now observing lineages that directly correspond with South Asian ancestors.
Even nations with clean water have not been immune; the CDC reported approximately 450 culture-confirmed typhoid cases in the United States in 2019, mostly linked to travel in recent times.
This presents a challenge for doctors, as existing treatment strategies may not address the imported H58 strain, which is often resistant to multiple antibiotics. Quick susceptibility testing, still not available in many areas, is becoming increasingly necessary.
Monitoring Typhoid Resistance
Without ongoing genomic surveillance, new resistant strains could cross borders undetected until health systems react too late. A 2022 study tracked nearly 8,000 S. typhi genomes to analyze their origins and migration, but such comprehensive data is still lacking in resource-limited regions.
Health policy needs to adapt rapidly. Countries facing rising resistance rates shouldn’t wait for full-blown outbreaks before implementing vaccination or treatment protocol adjustments. Quick responses rely on accurate data and empowered public health systems to act effectively.
Actions for Clinicians
Full courses of azithromycin, lasting between 10 to 14 days, remain effective in most situations, but follow-up cultures are essential. Skipping post-treatment monitoring can lead to silent carriers that reintroduce the disease into the community.
In areas where ceftriaxone MICs can be assessed, any upward trend should trigger public health alerts. Combination therapies, like using azithromycin with meropenem for severe cases, may mitigate further resistance but can drive up costs.
It’s crucial for physicians to report all instances of typhoid resistance and treatment failure, as aggregated data can expedite updates to national treatment guidelines more swiftly than peer-reviewed studies.
The Importance of Basic Safety Measures
Researchers are exploring new oral β-lactamase inhibitors that could enhance the effectiveness of inexpensive penicillins, but these advancements may take years. Similarly, phage therapy and resistant bacteria “decoys” show promise but are not yet proven.
For now, the most significant benefits arise from fundamental public health measures: ensuring access to safe water, developing sewer systems, and maintaining reliable refrigeration can reduce typhoid risk more effectively than any medication.
Investing even modestly in these areas yields benefits across multiple diseases—not just typhoid. This approach presents an undeniably strong argument for governments grappling with tight health budgets.
The findings are documented in the journal The Lancet Microbe.
