25 March 2025: Articles
Unexpected Deltoid Abscess from BCG Vaccination in a Healthy Adult: A Case Report
Challenging differential diagnosis, Diagnostic / therapeutic accidents
Ahmad Abdalla

DOI: 10.12659/AJCR.946723
Am J Case Rep 2025; 26:e946723
Abstract
BACKGROUND: The Bacillus Calmette-Guérin (BCG) vaccine is used to prevent tuberculosis in countries with high rates of tuberculosis. Although the vaccine is generally low risk, there are reports of minor local adverse effects. Rare complications such as abscess formation have been reported in immunocompromised and pediatric patients. However, reports of inoculation-site abscesses are exceedingly rare in the immunocompetent adult population, and there is no clear management plan that has been agreed upon for these cases. We present a case of a 30-year-old immunocompetent woman who developed a Mycobacterium tuberculosis complex abscess following intramuscular injection of the BCG vaccine.
CASE REPORT: A healthy 30-year-old woman came in for a MMR vaccination but mistakenly received the BCG vaccine intramuscularly in her left deltoid. One week later, she developed pain and swelling at the injection site. A MRI of her shoulder a week later revealed an intramuscular pseudo-lesion. An ultrasound done another 2 weeks later demonstrated an abscess. An acid-fast bacilli smear and culture were done using aspirated fluid and were negative. Pus began to drain from her shoulder days later, which returned positive on a smear and culture for pan-sensitive Mycobacterium tuberculosis complex. She recovered fully following 6 months of anti-tuberculosis medications (rifampicin, isoniazid, pyrazinamide, ethambutol).
CONCLUSIONS: Development of an abscess secondary to a vaccine should still be considered as a differential diagnosis for vaccine injection-site swelling in immunocompetent adult patients. Healthcare professionals should always confirm the correct type of vaccination and mode of administration before injection to avoid preventable vaccination complications.
Keywords: Abscess, Antitubercular Agents, BCG Vaccine
Introduction
The attenuated Bacillus Calmette-Guérin (BCG) vaccine is administered to prevent tuberculosis worldwide mainly for the pediatric population [1]. It was first created by Albert Calmette and Camille Guérin over a century ago, and the first human being was given the BCG vaccine in 1921 [1]. The vaccine contains a live, attenuated form of the bacteria,
Complications of BCG vaccinations are rare and generally non-severe. The most common complications include lymphadenopathy, ulceration of the inoculation site, residual scarring, and keloid formation [3]. Studies have shown that 0.001% of intradermal BCG vaccinations resulted in local complications in immunocompetent patients [3]. Factors such as the incorrect route of administration and an immunocompromised patient can increase the risk of complications from the BCG vaccine [4]. Rare complications of the BCG vaccine have been reported, primarily in the pediatric population, such as inoculation-site abscess [5,6], lymphadenitis, BCG osteomyelitis, and disseminated infection in the setting of an immunocompromised patient [3]. We present an unusual case of a deltoid abscess following intramuscular administration of the BCG vaccine in an immunocompetent woman.
Case Report
A 30-year-old woman with no past medical history was recommended to receive the MMR vaccine in an outpatient clinic. She mistakenly received the BCG vaccine intramuscularly in her left deltoid, and this error went unnoticed. The BCG vaccine she received was a freeze-dried variant that contained the live, attenuated
Two weeks after the BCG vaccine injection, a T2-weighted magnetic resonance imaging (MRI) scan was done on her shoulder, which showed an intra-deltoid pseudo-lesion with a high signal indicating edema and no definitive wall or fluid collection (Figure 1). An ultrasound scan done 2 weeks later suggested a thick-walled fluid collection with an estimated volume of 15 mL in the lateral aspect of the soft tissue of the upper arm, consistent with an abscess (Figure 2). To identify the pathogen responsible, she underwent fine-needle aspiration (FNA) of the lesion. A bacterial culture and an acid-fast bacilli (AFB) smear were done on the aspirated fluid, yet both tests returned negative. Yellow, purulent discharge began to drain from the left shoulder area 2 days following the FNA. This discharge was used for an AFB smear and culture with sensitivities. The auramine-rhodamine stain revealed yellow fluorescent bacteria, consistent with Mycobacteria (Figure 3). The liquid culture also returned positive for pan-sensitive
Two months following the initial BCG vaccine injection, first-line anti-tuberculosis medication – rifampicin (600 mg daily), isoniazid (300 mg daily), pyrazinamide (1500 mg daily), and ethambutol (1200 mg daily) – was started. The initial treatment was effective, and she recovered fully and reported no further symptoms 6 months after initiation of the anti-tuberculosis treatment. Another MRI scan was done during a follow-up 3 months after completion of anti-tuberculosis treatment, revealing a significant decrease in size of the BCG deltoid abscess (Figure 6).
Discussion
The BCG vaccine, when given intradermally to appropriate patients, is generally safe, with a low risk of complications [4]. These adverse events are usually self-limiting and restricted to the injection site [4]. Administration of the BCG vaccine intramuscularly is commonly the result of an error and can lead to rare and preventable complications, even in immunocompetent patients. On the other hand, the measles, mumps, and rubella (MMR) vaccine is normally given intramuscularly to patients. A reasonable explanation for the error in this case is that the healthcare professional administering the vaccine confused the BCG vaccine for the MMR vaccine and injected it intramuscularly. Furthermore, this case demonstrates a complication of erroneous intramuscular administration of the BCG vaccine; only a few cases of this type of incident have been recorded in the literature [4–6].
Erythema and swelling of the shoulder is a symptom of various infectious and non-infectious differential diagnoses, such as a hematoma, bursitis, or cellulitis. It can be difficult to diagnose rare conditions, especially when a much more common diagnosis presents similarly. Our patient was initially suspected to have cellulitis on her shoulder, but the diagnosis was revised after a treatment course of cefuroxime proved to be ineffective. Development of suppurative adenitis, inoculation-site abscess, type IV granulomatous hypersensitivity reaction, secondary bacterial infections, and intramuscular abscess secondary to BCG vaccination have been reported in the pediatric population [5–8], most commonly in immunocompromised patients. In our patient, an abscess secondary to the BCG vaccine would at first appear to be a very unlikely diagnosis considering that the patient was a healthy immunocompetent adult, in contrast to the cases in the literature.
Although the diagnosis of an abscess secondary to the recent BCG vaccination could have been made on clinical grounds, microbiology laboratory tests can be extremely useful; the diagnosis of an intramuscular abscess due to a BCG vaccine was confirmed in this case only after cultures using abscess discharge returned positive for a
Conclusions
Abscess formation following a BCG vaccination is a rare complication, yet certain factors, such as an immunocompromised status and incorrect vaccine administration technique, increase the risk of BCG vaccine complications. Although there is no consensus on the optimal management of an abscess secondary to a BCG vaccine, anti-tuberculosis antibiotics appear to have played a significant role in the treatment of this patient. Strategies to prevent complications from the BCG vaccine include adequate training in vaccine administration and medication identification skills.
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References:
1.. Okafor CN, Rewane A, Momodu II, Bacillus Calmette Guerin. [Updated 2023 Jul 3].: StatPearls [Internet], 2025, Treasure Island (FL), StatPearls Publishing Available from: https://www.ncbi.nlm.nih.gov/books/NBK538185/
2.. Tobin EH, Tristram D, Tuberculosis overview. [Updated 2024 Dec 22].: StatPearls [Internet]., 2025, Treasure Island (FL), StatPearls Publishing Available from: https://www.ncbi.nlm.nih.gov/books/NBK441916/
3.. Bolger T, O’Connell M, Menon A, Butler K, Complications associated with the bacille Calmette-Guérin vaccination in Ireland: Arch Dis Child, 2006; 91(7); 594-97
4.. Pasteur MC, Hall DR, The effects of inadvertent intramuscular injection of BCG vaccine: Scand J Infect Dis, 2001; 33(6); 473-74
5.. Sedighi P, Sadrosadat ST, Movahedi M, Sedighi I, BCG-Induced cold abscess as a complication of inadvertent vaccine injection: A case series: Clin Case Rep, 2022; 10(4); e05711
6.. Al Namshan M, Oda O, Almaary J, Bacillus Calmette-Guérin-related cold thigh abscess as an unusual cause of thigh swelling in infants following BCG vaccine administration: A case series: J Med Case Rep, 2011; 5; 472
7.. Gautam U, Shrestha AL, Mishra A, Suppurative complications following BCG vaccine in 2 Nepalese children: Ann Med Surg (Lond), 2022; 76; 103484
8.. Keijsers RR, Bovenschen HJ, Seyger MM, Cutaneous complication after BCG vaccination: Case report and review of the literature: J Dermatolog Treat, 2011; 22(6); 315-18
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