Imaging bacterial infection with (99m)Tc-ciprofloxacin (Infecton)

Abstract

Aims: The diagnosis of deep seated bacterial infections, such as intra-abdominal abscesses, endocarditis, and osteomyelitis, can be difficult and delayed, thereby compromising effective treatment. This study assessed the efficacy of a new radioimaging agent, Tc-99m ciprofloxacin (Infecton), in accurately detecting sites of bacterial infection.

Methods: Eight hundred and seventy nine patients with suspected bacterial infection underwent Infecton imaging and microbiological evaluation. The sensitivity and specificity of Infecton in detecting sites of bacterial infection were determined with respect to Centres of Disease Control, World Health Organisation, and Dukes's criteria.

Results: Five hundred and seventy four positive and 295 negative images were produced. These included 528 true positives, 46 false positives, 205 true negatives and 90 false negatives, giving an overall sensitivity of 85.4% and a specificity of 81.7% for detecting infective foci. Sensitivity was higher (87.6%) in microbiologically confirmed infections.

Conclusions: Infecton is a sensitive technique, which aids in the earlier detection and treatment of a wide variety of deep seated bacterial infections. The ability to localise infective foci accurately is also important for surgical intervention, such as drainage of abscesses. In addition, serial imaging with Infecton might be useful in monitoring clinical response and optimising the duration of antimicrobial treatment.

Figure 1

Patient with a surgical sternal split and mitral valve replacement developed fever, with positive blood cultures. Tc-99m Infecton images at one and four hours, left anterior oblique views of the heart. Left hand image: at one hour there is intense uptake in the sternum and a normal cardiac blood pool. Right hand image: at four hours there is still intense uptake in the sternum. Instead of the blood pool activity fading, there remains a focus of increased uptake in the mitral area. It was concluded that there is infection not only in the sternum but also in the prosthetic mitral valve. This was confirmed microbiologically after surgery.

Figure 2

A man of 54 developed a painful swollen left index finger as a result of an infected interphalangeal joint. Tc-99m Infecton imaging was performed on two occasions three months apart. (A) A set of blood pool, 1, 3.5, and 24 hour images show focally increased and persistent uptake in the left index finger. (B) Three months after antibiotic treatment, the early image still shows increased uptake in the left index finger. This is slightly less at four hours and has faded completely by 24 hours. It was concluded that the infection in the left index finger had resolved, leaving some residual inflammatory arthropathy. This demonstrates the importance of the 24 hour image to distinguish septic from inflammatory arthropathy.