Discussion and Conclusion
Thigh swelling is a clinical sign of various infectious or noninfectious underlying causes. Regarding the patients’ physical examination cold abscess was the most probable diagnosis since patients did not have considerable warmness, erythema, and other signs of inflammation at presentation. Mycobacterial infection is the most common cause of cold abscess (6), so acid-fast staining was done along with routine culture and was positive. Furthermore, a PCR test was done for confirmation of diagnosis which was positive for Mycobacterium Bovis.
BCG is derived from live attenuated Mycobacterium Bovis and according to the expanded program of immunization (EPI) in Iran, all children receive BCG vaccination after birth (8). BCG is routinely injected intradermally over the deltoid muscle. The abscess location in all patients was in the anterior thigh muscle, the exact site of vitamin K and Hepatitis B vaccine injection at birth. The positive PCR test for BCG Mycobacterium Bovis and the abscess location raised the possibility of erroneous injection of BCG vaccine into the infants’ thigh muscle. We checked the hospitals where case 2 and case 3 were born and found out that vitamin K is injected by the midwife after that, BCG and hepatitis B vaccine is injected by the vaccinator so the most probable situation is the injection of 0.5 ml of BCG intramuscularly to the left thigh instead of hepatitis B vaccine (Hepatitis B vaccine is routinely injected to the left thigh). In case 1, regarding the presence of swelling in the right thigh, probably 0.5 ml of BCG is injected intramuscularly instead of vitamin K at birth (vitamin K is routinely injected to the right thigh). The injection of a high dosage of BCG, 0.5 cc instead of 0.05 ml, and intramuscular injection instead of intradermal are both factors for BCG-related abscess which is observed in these cases. Similar cases of BCG-induced cold abscesses are reported in Saudi Arabia and India. Verma et al. reported a four-month-old girl from India. The patient presented with a swelling on the anterolateral side of her left thigh since receiving an intramuscular Diphtheria, whole-cell Pertussis, and Tetanus (DwPT) vaccine injection at the age of six weeks. Fine needle aspiration of the lesion showed caseating granuloma and staining for acid-fast bacilli was positive. The most probable cause of the abscess, in this case, is thought to be following erroneous BCG injection instead of DwPT vaccine, and the diagnosis is not confirmed since the PCR test for BCG Mycobacterium Bovis was not done. This type of error is not considered for our cases because the BCG vaccine is not available in vaccination centers in Iran and the error can only occur in hospital settings while vaccine injection at birth. The article has mentioned that the swelling was completely healed in six months without any anti-mycobacterial therapy. But, we preferred to start treatment to speed up healing and to prevent further complications (9). Also, Namshan et al. reported five similar cases of BCG-induced cold abscess from Saudi Arabia. They did not perform a PCR test for BCG Mycobacterium Bovis and the diagnosis was based on culture results. Three cases received anti-mycobacterial drugs and finally, all cases were healed without remarkable problems during a two-year follow-up (6). The most extensive report is from Saudi Arabia with 25 cases of BCG-induced abscess as a result of technical errors during vaccine injection. The diagnosis was based on a positive smear for acid-fast bacilli for all cases and a positive culture for 17 cases. Nowadays, PCR test can detect the exact organism and help us for an accurate diagnosis. In the later study the exact source and route of infection was unknown but we tried to find where the error originates from (10). Our recommendation to prevent this error is to assign separated staff to inject each of the vaccines, injection of BCG and hepatitis B vaccine in different rooms, and checking the vaccine injection by a second observer. Also, WHO has warned that the correct and precise BCG vaccine injection technique by trained staff is important for optimal efficacy and safety of the vaccine (1).