From sexually transmitted infections to tick-borne diseases, the complete blood count has become a frontline tool in modern diagnosis and treatment.
By Jim Poggi
In the Repertoire September 2025 Physician Office column “Hidden Dangers,” we looked at infections that do not present obvious physical symptoms and how the complete blood count (CBC) can come to the rescue and uncover these hidden dangers.
In this column, I intend to point to the history of diagnosis and treatment for these infections, and how we have just barely managed to make progress in uncovering and treating them. The complete blood count and microbiology will take center stage as we look at advances in diagnosis of infection and appropriate treatment. This column will also provide concrete evidence that ‘it can happen here,’ giving you a way to counter a common customer objection – especially when it comes to sexually transmitted infections (STIs). Let’s start by looking at the past.
The “germ theory of disease” is discovered
Think back to a time long ago, before your grandparents were born. Our ancestors were still a bit furrier than today. They lived in trees and often fell out of them. Dogs were not yet domesticated. There were infections even then, mostly obvious ones related to injuries from predator bites and falling out of trees. They were diagnosed by the sore red area and associated inflammation.
What did our ancestors do? They rubbed various plant-derived substances on the affected area and hoped it would go away. Sometimes it worked, sometimes we lost a member of the clan. No one thought of infections they did not see. That was far less important than foraging for food and avoiding being the next meal for predators.
We have come a long way since then. We have left the trees and finally domesticated dogs, or perhaps they have domesticated us. A very important move forward made a difference in our understanding and cure of infections, whether they were visible or not. Two pioneering microbiologists, Louis Pasteur and Robert Koch, proposed the “germ theory of disease” in the 19th century, which has been the cornerstone of our understanding of what causes an infection.
But, what to do about it? We were still rubbing various plant-derived substances on the affected area until the first antibiotic, penicillin, was made widely available after World War II. While Alexander Fleming discovered penicillin in 1928, it took years for it to become widely available in developed countries. There are still gaps in availability of antibiotics in less developed countries.
How many annual infections occur in the U.S.?
As we fast forward to more modern times, what is the latest story on infections in the U.S., and should we be worried? The Centers for Disease Control and Prevention (CDC) reports an acknowledged total of about 110 million infections confirmed in 2023. They also acknowledge that there are any number of infections that do not go reported.
It is my assessment that many of these less serious infections are cured by rubbing or spraying plant derived substances (and topical antibiotics) on the affected area. Within this data, most infections are visible or at least obvious. Food-borne infections made up the largest group at 48 million, followed by respiratory infections annually ranging from 30 to 40 million. Not so obvious are STIs at 26 million. That leaves another 5 million difficult to diagnose enteric infections (appendicitis, pancreatitis, gall bladder rupture and peritonitis).
Overall, if our ancestors looked at the situation, they would observe that three out of every 10 infections did not exist since they were not visible or obvious. No wonder the mortality rate was not just comprised of predator attacks and falls out of trees. There were several causes that simply could not be acknowledged or explained. There was little that even the local shaman could do in this case.
Infections you can’t see
While the ability to identify obvious infections and to effectively cure them was vastly improved by the middle of the 20th century, what about the less obvious internal infections our ancestors did not understand? How have they been diagnosed?
Sometimes it has been a simple matter of tracing the incidence of the spread of STIs from “patient zero” to their sexual partners. This was a common practice that began in the early 20th century and is still practiced today, especially as the variety of STIs and their incidence has increased.
But, there is a difference between suspecting a patient has an STI and being able to prove they have an STI. What to do?
CBC and microbiology power diagnosis and treatment
Here is where the CBC and modern microbiology come to our rescue. The CBC can not only confirm that a patient has an infection, but it can also identify whether this infection is bacterial or viral. This is a massive step forward, not just for effective patient treatment, but also for the practice and promotion of antibiotic stewardship.
Even if we do not consider enteric or respiratory infections, STIs alone can be caused by either bacterial or viral agents. Think of two STIs that are currently on the rise. Syphilis is caused by a bacterium and AIDS is caused by a virus. Treatment plans are entirely different for each of these organisms. So, the ability to determine whether the patient has an infection that is not obvious, and then to understand whether it is bacterial or viral, are fundamental underpinnings of infectious disease treatment in the U.S. today.
The CBC is the most effective means of making this determination. An increase in white blood cell count (WBC) is the first indication of an infection. Then it is important to identify whether an infection is viral or bacterial. That’s where the CBC differential comes into play. Typically, an increase in neutrophils, the most common WBCs, indicates a bacterial infection. An increase in lymphocytes more often points to a viral infection. An increase in eosinophils can point to an allergy and lead to a different path to diagnosis. While infections can be complicated, the CBC is not. In a minute or less the lab receives at least 11 different parameters that can point to general health concerns (hemoglobin and hematocrit are examples that may indicate anemia or a bleeding disorder) or an infection, with the WBC differential well established as the gold standard for initial screen for an infection. As important, once a treatment program has begun, follow up with a CBC can demonstrate the effectiveness of the treatment.
Microbiology plays its part by identifying the specific etiologic agent and identifying which antibiotics are most likely to be able to treat it effectively if it is bacterial. The combination of CBC and microbiology is an effective “one-two punch” in identifying whether the patient has an infection that is not obvious, then taking the next step to identify the organism and the proper antibiotic treatment to effectively cure it. Advances in molecular diagnostic technology are rapidly improving the speed and accuracy of traditional microbiology methods of identification of these microorganisms.
STIs and other pesky infections
While STIs are unfortunately on the rise, they are by no means the only infections that are not obvious. Enteric diseases (diseases of the gastrointestinal tract) can present with slowly increasing severity and many have similar symptoms. The CBC can identify whether the symptoms are due to an infection or another cause such as reflux esophagitis and lead to further discovery to identify the specific cause.
Tick-borne illnesses including Lyme disease, babesiosis, anaplasmosis, ehrlichiosis and Rocky Mountain Spotted fever are spreading due to the expansion of their environment due to global warming. Most of these diseases start out in ways our ancestors would understand – as a sore, red-inflamed bite. Eventually the soreness goes away, but the bacteria remains in the patient’s system, and can cause serious systemic diseases over time. Not obvious, right? Not to the naked eye once the sore area clears, but a CBC as follow up to the infected bite can determine whether an infection is still present, or has cleared up all by itself, or by the patient successfully rubbing plant derived substances on it. Tick-borne illnesses are moving to larger areas of the U.S. and becoming more common as more Americans encounter the larger population of ticks outdoors. This presents a new challenge to the U.S. healthcare system and physician practices everywhere. The CBC as a follow up to tick infection is a sensible way to assure that these illnesses do not progress to serious diseases that are harder to cure effectively.
The payoff
So, where does all this lead us? As trusted consultants to our customers, we have no doubt presented the case for including the CBC in our customers’ arsenal of diagnostic tools. Some have agreed. Others remain unconvinced. Take the leap of faith and present the information regarding infections that are not obvious and initiate the conversation again with customers that have not yet initiated CBC testing. Bringing along statistics on the significant growth of STIs, from those that are clearly associated with serious after effects to those that are not as clearly associated with significant morbidity and mortality.
At the end of the day, infections are all around us, whether they are obvious or not. Are your customers prepared to deal with them? They are if you have armed them with the information they need to understand the incidence and significance of infections they cannot see and have helped them to adopt the CBC.
What are you waiting for? Share this information with your trusted hematology manufacturer, make a list of your customer prospects and start making calls. After all, we have made a lot of progress since we left the trees, even though we continue to rub plant derived substances on many red, swollen areas.
There is plenty of more work to do. Get out there and help combat the infections you can’t see.
Residual infections
One note on the utility of the CBC. Many diseases, most notably COVID, appear to be cured. Cough, fever, wheezing and obvious symptoms go away.
But sometimes there is still a residual infection. The data is just making it clear, but “long COVID” is now recognized as a disease itself. A CBC is an excellent means of follow-up for these patients for your customers to know for sure whether the infection has been cleared or whether further treatment is required.
Further information
To view excellent CDC information visit www.cdc.gov/sti/php/communication-resources/prevalence-incidence-and-cost-estimates.html
For those who insist “it can’t happen here”, visit www.ncbi.nlm.nih.gov/books/NBK573159.
Depending on where you line up, figure 2-3 and 2-8 show very clearly that, yes, it can happen here.