Unmasking the silent invader: A rare encounter of Neisseria gonorrhoeae in joint fluid

To the Editor

A 36‐year‐old male patient presented to the hospital with pain and swelling in his left knee. His examination revealed hemoglobin levels of 11.9 g/dL, red blood cell (RBC) counts of 3.64 × 10⁶/μL, white blood cell (WBC) counts of 17 × 10³/μL and platelet counts of 673 × 10³/μL. The serum levels of alanine aminotransferase were higher than the normal range at 59 IU/L (reference range: 7–52 IU/L). The erythrocyte sedimentation rate (ESR) value obtained was significantly elevated at over 140 mm/h (reference range: 0–15 mm/h).

The patient presented with a 4‐day history of pain, effusion, and swelling in the left knee. The affected joint was warm to the touch and exhibited signs of inflammation during the physical examination, such as erythema and joint effusion. During a focused sexual history interview, the patient disclosed that they had engaged in sexual activity with multiple partners without using protection approximately a month ago.

Microscopic examination of the synovial fluid revealed a markedly elevated count of RBCs and total nucleated cells, with a predominance of neutrophils. These findings were further supported by the presence of elevated inflammatory markers, including significantly increased levels of WBC and ESR. Additional investigations, such as microbiological cultures, were performed on the synovial fluid. The culture plates were incubated in a humidified atmosphere with 5%–10% carbon dioxide at a temperature of 35–37°C for 24–48 h. Microbiological cultures were performed on the synovial fluid, and subsequent cultures revealed the growth of small, grayish, translucent colonies on chocolate agar (Figure 1A). The Gram stain of the clinical specimen revealed the presence of Neisseria gonorrhoeae. The findings showed characteristic Gram‐negative diplococci, which appeared as pairs of cocci arranged in an intracellular manner (Figure 1B). In addition, the identification of N. gonorrhoeae was performed using the API® NH system. Isolated bacterial colonies suspected to be N. gonorrhoeae were inoculated into the API® NH system using the standard laboratory protocols. Based on the provided interpretation guide, we observed specific reactions and color changes in the API® NH strip wells, which indicated the presence of N. gonorrhoeae (Figure 1C). These reactions were consistent with the known biochemical characteristics of N. gonorrhoeae. In the case presented, the patient received medical treatment for N. gonorrhoeae infection, which involved a combination of antibiotics: ceftriaxone (2 g, administered intravenously once daily) and azithromycin (two tablets, taken once daily). After starting antibiotic therapy, the patient showed a positive response and improvement in clinical symptoms.

FIGURE 1.

Neisseria gonorrhoeae growth on chocolate agar. (A) Colonies of N. gonorrhoeae on chocolate agar show a small, translucent, and smooth morphology with a grayish‐white color. (B) Gram staining of bacterial smears from the colonies reveals characteristic Gram‐negative diplococci morphology. These findings confirm the presence of N. gonorrhoeae in the cultured sample. (C) API® NH strip results for the identification of N. gonorrhoeae. The API® NH strip reactions are shown for each well (W1–W13) of the strip. Positive reactions are indicated by a color change. (W1: penicillinase positive, W2: glucose positive, W3: fructose negative, W4: maltose negative, W5: sucrose negative, W6: ornithine decarboxylase negative, W7: urease negative, W8: lipase negative, W9: alkaline phosphatase negative, W10: β‐galactosidase negative, W11: proline arylamidase positive, W12: gamma glutamyl transferase negative, W13: indole negative). These reactions confirm the presence of N. gonorrhoeae in the tested sample, consistent with the known biochemical characteristics of the pathogen.

N. gonorrhoeae is a Gram‐negative, coffee‐bean‐shaped intracellular diplococcus responsible for the sexually transmitted infection gonorrhea. ¹ In Taiwan, gonorrhea has been classified as a notifiable communicable disease since the 1950s. The incidence of the disease has increased from 9.79 cases per 100,000 population in 2010 to 19.00 cases per 100,000 population in 2016. ² , ³ Extra‐genital manifestations of gonococcal infections are uncommon. Disseminated gonococcal infection are generally regarded as rare, with a prevalence rate estimated to be between 0.5% and 3% among cases of N. gonorrhoeae infection. ⁴ , ⁵

This case report presents a patient with N. gonorrhoeae infection in their joint fluid, emphasizing the importance of considering this pathogen as a potential etiology in patients who exhibit joint symptoms, especially in sexually active individuals. Understanding the clinical presentation, diagnostic evaluation, and management of gonococcal arthritis is essential for timely diagnosis and optimal patient outcomes.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflict of interest.

ETHICS STATEMENT

Ethics approval was obtained from the Institution Review Board of China Medical University Hospital (CMUH112‐REC‐008).