By Dr Ntokozo Mzimela — Pathologist (Microbiology), Lancet Laboratories, in conversation with Clive Maistry
Dr. Ntokozo Mzimela chats with Clive Maistry about recent outbreaks and what South African clinicians need to know
Clive Maistry: Ntokozo, you mentioned you had an interesting conversation recently that got you thinking about Legionella. Tell me what happened.
Dr. Ntokozo Mzimela: Absolutely, Clive. So I was catching up with a friend who works on a cruise ship – you know how many South Africans end up working on these international vessels. She casually mentioned that the CDC had announced Legionella outbreaks on cruise ships. My microbiologist brain immediately went into overdrive because, let’s be honest, cruise ships are massively popular with South Africans. We love our international holidays, and cruises are often the dream trip.
Clive: That would definitely catch my attention too. What did you find when you started digging?
Dr. Mzimela: That’s when I found this Guardian article titled “New York City declares Harlem legionnaire’s disease outbreak over.” So here I am looking at two separate but connected stories – cruise ship outbreaks affecting international travelers and a major urban outbreak that just concluded. It made me realize we need to have a proper conversation about Legionella, especially with our holiday season approaching.
Clive: Right, because December holidays are when many South Africans travel internationally. What exactly happened with these outbreaks?
Dr. Mzimela: The numbers are quite sobering. The CDC documented 12 cases of Legionnaires’ disease on two cruise ships between November 2022 and June 2024. What’s particularly concerning is that this was the largest cruise-associated outbreak the CDC had investigated since 2008. Meanwhile, the New York outbreak resulted in 114 cases and seven deaths in Central Harlem.
Clive: Seven deaths? That’s serious. What was the source?
Dr. Mzimela: Here’s what’s really concerning – the cruise ship cases were traced to private balcony hot tubs. You know, those luxury amenities that people pay extra for. These hot tubs were operating for months with water temperatures between 25-45°C – perfect for Legionella growth – without proper draining or disinfection. The New York outbreak was linked to cooling towers on building rooftops.
Clive: For our readers who might need a refresher, can you explain what we’re dealing with here?
Dr. Mzimela: Certainly. Legionella pneumophila is a gram-negative, aerobic bacterium that’s quite clever in how it survives. It loves warm, stagnant water systems – cooling towers, hot tubs, decorative fountains, complex plumbing systems. The thing that makes it particularly dangerous is how it spreads: people get infected by breathing in water vapor containing the bacteria. No person-to-person transmission, but that means environmental sources can affect multiple people simultaneously.
Clive: So if someone comes back from a cruise or overseas trip with pneumonia-like symptoms, Legionella should be on our differential?
Dr. Mzimela: Absolutely. The symptoms mimic other types of pneumonia – fever, chills, muscle aches, cough, shortness of breath. But here’s the clinical pearl: Legionnaires’ disease can progress rapidly to severe pneumonia. If left untreated, we’re looking at potential shock and multi-organ failure.
Clive: Who’s most at risk?
Dr. Mzimela: Great question. In the NYC outbreak, about 90% of those affected had known risk factors: smoking, compromised immune systems, chronic lung disease, other chronic conditions, or being 50 and older. So our typical vulnerable populations, but the travel component means we might see this in otherwise healthy people who’ve been exposed during their holidays.
Clive: From a diagnostic perspective, what tools do we have available in South Africa?
Dr. Mzimela: We have several excellent options. First, the Legionella urinary antigen test – it detects L. pneumophila serogroup 1, which is the most common. It’s rapid and specific, and many of our private labs can do this. However, it only catches serogroup 1, so we can’t rely on it alone.
Clive: What about culture?
Dr. Mzimela: Culture on selective media remains our gold standard, especially for detecting other serogroups and species. But here’s the thing – Legionella can be quite difficult to grow. It requires special media, specific conditions, and can take several days. Even with optimal conditions, we sometimes miss cases because the organism is fastidious.
Clive: So what’s the solution?
Dr. Mzimela: This is where molecular techniques have really revolutionized our approach. At Lancet, we offer comprehensive respiratory panels that include Legionella detection using molecular methods. Instead of waiting days for culture results that might be negative despite active infection, we can get results much faster and with excellent sensitivity.
Clive: How does that work practically?
Dr. Mzimela: It’s straightforward for clinicians. You send a sputum sample for our respiratory panel, and we use molecular techniques to detect not just Legionella, but a whole range of respiratory pathogens simultaneously. This is particularly valuable when you’re dealing with a patient who has pneumonia and you’re not sure of the cause – you get comprehensive coverage including Legionella, along with other bacterial and viral pathogens.
Clive: That sounds much more practical than trying to decide between individual tests.
Dr. Mzimela: Exactly. And the molecular approach doesn’t have the same growth requirements as culture, so we’re not dependent on organism viability or optimal transport conditions. It’s especially useful for those travel-associated cases where you might suspect Legionella but want to rule out other possibilities as well.
Clive: You mentioned travel history being important. How should we approach this?
Dr. Mzimela: This is critical, especially for our South African context. We need a thorough travel history of all destinations during the 10 days before symptom onset. That cruise to the Mediterranean? The business trip to New York? The holiday in Dubai with those amazing hotel pool areas? All relevant. About 10% of all Legionnaires’ disease cases occur in people who’ve traveled during this window.
Clive: What about local sources? Should we be worried about Legionella in South Africa?
Dr. Mzimela: Definitely. While we might not have the cooling tower density of New York City, we have plenty of potential sources. Think about our hotel industry, shopping malls with complex air conditioning systems, luxury resorts with decorative fountains and spas. Even some of our private hospitals have sophisticated water systems that could harbor Legionella if not properly maintained.
Clive: That’s a sobering thought. What should clinicians be doing differently?
Dr. Mzimela: First, maintain a high index of suspicion, especially during our peak travel seasons – December holidays and Easter. If someone presents with pneumonia that’s not responding to typical community-acquired pneumonia treatment, think Legionella. Don’t rely solely on urinary antigen testing – culture when indicated.
Clive: What about treatment?
Dr. Mzimela: The good news is that Legionnaires’ disease responds well to appropriate antibiotics when caught early. Fluoroquinolones or macrolides are typically first-line. The key is early recognition and prompt treatment. Complications are much less likely when we start treatment early.
Clive: Any specific advice for the upcoming holiday season?
Dr. Mzimela: Great question. For our patients planning cruises or international hotel stays, especially those in high-risk categories, they should be aware of the risks. If they develop respiratory symptoms within 10 days of returning from travel, they should seek medical attention promptly and mention their travel history.
Clive: What about from a public health perspective?
Dr. Mzimela: We need to think about clusters. These can be difficult to detect because travelers often return home before symptoms develop. That “isolated” case might not be isolated at all. The CDC actually requests notification of travel-associated cases, and I think we should consider similar reporting here in South Africa.
Clive: You mentioned both outbreaks led to changes. What happened?
Dr. Mzimela: Both cruise lines modified their hot tub operations – they removed heating elements, now only fill tubs on guest request, drain between uses, and clean more frequently. New York City has proposed new cooling tower regulations. It’s reactive, but necessary.
Clive: What’s your take on the bigger picture?
Dr. Mzimela: Look, Legionella isn’t going anywhere. As long as we have complex water systems – and as long as South Africans love to travel and enjoy these amenities – we’ll see cases. Our role is to stay vigilant, maintain our diagnostic skills, and remember that behind every positive test is a patient who needs prompt treatment.
Clive: Any final thoughts for our readers?
Dr. Mzimela: The cruise outbreaks remind us that luxury can harbor danger. The NYC outbreak shows that even well-regulated environments can have problems. But here’s the encouraging part – when we combine good clinical practice with proper public health response, these outbreaks can be controlled. The NYC mayor noted that residents can “breathe a sigh of relief” now that it’s over.
Clive: So the message is stay curious, stay vigilant?
Dr. Mzimela: Exactly. Sometimes the most important diagnostic question isn’t “What organism is this?” but “Where has this patient been?” Especially for us in South Africa where international travel is such a big part of many people’s lives.
Clive: Any experiences with Legionella cases you can share?
Dr. Mzimela: I’ve seen a few travel-associated cases over the years – usually picked up when clinicians were astute enough to ask about travel history and think outside the box. The key is maintaining that index of suspicion.
Clive: Thanks for this conversation, Ntokozo. Really valuable insights for our readers.
Dr. Mzimela: Thanks, Clive. I hope this helps our colleagues think about Legionella in their practice, especially as we head into travel season. And remember, we’re always available at Lancet for consultation on complex cases.
Dr. Ntokozo Mzimela is a Pathologist in Microbiology at Lancet Laboratories, covering the South and East Region of Johannesburg.