For decades, as medical researchers have sought new treatments to battle the deadly HIV virus, clinicians and public health officials have been working in tandem to limit not only the spread of HIV, but diseases that can emerge as co-infections, especially sexually transmitted diseases (STDs) such as syphilis, gonorrhea and Chlamydia. The reason for this has to do with the troubling reality of co-infections: HIV/AIDS makes people more vulnerable to STD transmission - and vice versa.
The CDC recommends regular co-infection tests for sexually active HIV-infected patients about every three to six months. In practice, said sources interviewed for this article, clinicians often prescribe such tests on a case-by-case basis. A physician likely will order tests for co-infections if an HIV patient seems to maintain a lifestyle that makes him or her vulnerable to STDs or if he or she shows symptoms, such as lesions, that suggest the presence of an STD.
"We see lots of co-infections in the HIV population, most likely due to a combination of increased susceptibility, immune system dysfunction and lifestyle," says Alan Wu, PhD, chief of the clinical chemistry/toxicology laboratory at San Francisco General Hospital, the main public healthcare facility in a city with a large population of men who have sex with men (MSM). Similarly, he says, people with STDs are more susceptible to HIV and other infections, as well as certain cancers, because of the likelihood of having inflammation or lesions - which act as ports of infiltration.
Battery of Tests
How often are HIV patients tested and for what? One might expect testing practice to follow co-infection incidence and prevalence trends among the U.S. population. A CDC fact sheet lists the Human papillomavirus (HPV) as the most common type of sexually transmitted infection in the U.S. In order, this is followed by Chlamydia, Trichomoniasis, gonorrhea, Herpes simplex virus 2 (HV-2), syphilis, HIV and hepatitis B. But testing among the HIV population does not necessarily mirror national STD trends, according to a paper published in April by the Medical Monitoring Project.2
The study shows that during a two-year period (2008-10), 55% of sexually active HIV patients in the U.S. were tested at least once in 12 months for syphilis while 23% and 24% underwent at least one test for gonorrhea and Chlamydia, respectively. The HIV surveillance program records and analyzes patient data from 23 participating geographic areas that represent about 80% of HIV/AIDs cases in the U.S.
The disparity between STD trends and testing practice is due in part to a testing bias in the study, but it also likely reflects the susceptibility of HIV patients to certain STDs and the distinct pathogenesis of STDs such as syphilis, said Pragna Patel, MD, MPH, a senior medical epidemiologist at the CDC who has worked for decades on HIV-related treatment and public health initiatives. For these, she said, there is a need for regular monitoring so that a co-infection is caught before it presents in an aggressive form.
"Syphilis usually presents as an ulcer and is easy to treat," Patel said. "Secondary syphilis is a more systemic infection, meaning it has spread through the body. Syphilis can be latent in that it exists in the body but hasn't caused symptoms. Now that HIV patients are living much longer because of the treatments we have, a clinician needs to be mindful that these infections could be with them a very long time. You need to test on a regular basis so you don't miss something that may be important to treat."
Patients deemed to be at risk of HIV infection give serum samples that will be tested with an antibody-detecting immunoassay. Initially, a physician may order a point-of-care test in the ED - the so-called "rapid tests" used in California and elsewhere. However, to comply with CDC's recommended test protocol, a hospital must do confirmatory laboratory testing.
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Once an infection has been detected, however, it's all about testing to determine viral load, subtype of HIV infection and the presence of co-infections that may further compromise the patient's health. Viral load testing may occur several times, while the use of a genotyping test, such as nucleic amplification (NAT), to determine HIV subtype is generally a one-off. But testing for co-infections, sometimes with a POC rapid test, will occur with some regularity as long as the HIV patient is alive and susceptible.
HIV co-infections go far beyond STDs. Among common non-STD co-infections are pneumocystis pneumonia (PCP), karposi sarcomas and hepatitis C. A healthy person exposed to some of these diseases has an immune system that will protect him or her from infection. For example, PCP is caused by a common fungus likely spread through the air and is easily defeated by a healthy immune system. But an AIDS patient with a weakened immune system may experience inflammation and fluid buildup in the lungs. It's just one more reason that a smart clinician will keep on testing.
Robert Kapler works as a freelance journalist, copy writer and marketing consultant for Bio-Rad Laboratories.
1. CDC Fact Sheet http://www.cdc.gov/std/stats/sti-estimates-fact-sheet-feb-2013.pdf
2. Flagg EW, et al. Bacterial sexually transmitted infections among HIV-infected patients in the United States: Estimates from the medical monitoring project. Sex Transm Dis. 2015 Apr;42(4):171-9. Abstract available at http://www.ncbi.nlm.nih.gov/pubmed/25763669