Posts Tagged ‘epidemiology’

An enemy returns: East of the Sun and far West of the Nile

Friday, July 19th, 2013
epidemic warnings come late; prevention is better

epidemic warnings come late; prevention is better

We came home from a short trip to Texas and I realized my weekly copy of JAMA had four articles on West Nile disease, its complications and possible prevention. After several years of relative quiescence, West Nile was back with a vengeance in 2012. Between the original New York City outbreak in 1999 and 2010 the virus has been endemic in the United States with intermittent flares, overall infecting an estimated three million Americans, causing West Nile fever (WNF) in 780,000, the much more severe West Nile neuroinvasive disease (WNND: e.g., involving the brain and other portions of the nervous system)  in 16,196 and killing 1549 of those.

Until 1999, the West Nile virus lived, mostly in birds, in Africa, Europe and Asia, but was not known to be in the Western Hemisphere. Its hosts (reservoirs) were bitten by mosquitoes whose name comes from the Spanish or Portuguese for "little fly," but some think this insect is the most dangerous creature on earth as it also transmits malaria, yellow fever and a variety of encephalitis-causing illnesses (inflammation of the brain). The mosquito in turn can pass the virus on to another bird or to a human

A 2001 article in the New England Journal of Medicine reviewed the original Western Hemisphere outbreak, the 1999 epidemic in New York City. It began with two patients hospitalized for encephalitis in the New York City borough of Queens. A preliminary epidemiologic search of nearby hospital admissions revealed six more cases. All eight lived in a sixteen square mile area in northern Queens and all had participated in evening outdoor activities (e.g., working in their gardens).

A search of their environments showed breeding sites for the particular species of mosquitoes known to carry St. Louis encephalitis (its vector), so the mini-epidemic was presumed to be an arthropod-bourne disease (The term arthropod include insects, spiders and crustaceans such as lobsters and crabs.) Mosquito control measures were promptly begun.

Eventually fifty-nine New Yorkers were hospitalized in August and September of that year with this outbreak. Although their ages varied from 5 to 90, the median age of these severely ill patients was 71 (NB. The "mean" is the "average" you're used to, where you add up all the numbers and then divide by the number of numbers. The "median" is the "middle" value in the list of numbers, so in this case there were as many patents over 71 and under that age).

The overall attack rate of West Nile in this outbreak went sharply up with age. Nearly two-thirds of those affected had encephalitis with altered mental status along with fever and abnormalities in their cerebrospinal fluid (CSF, the fluid that cushions the brain and spinal cord, bring it nutrients and removes waste products). Some of those had moderate to severe muscle weakness and/or meningitis (inflammation of the membranes that cover the brain and spinal cord) with fever, abnormal CSF findings, headache and stiff neck symptoms.

Seven of the fifty-nine (12%) of those with the disease died and those over age 75 were especially prone to death in this epidemic. Diabetes was another risk factor for mortality.

At the same time, there was a seemingly unrelated fatal illness occurring in the area's birds, especially in crows. The connection initially was missed as St. Louis encephalitis doesn't usually kill off its avian reservoir hosts.

Eventually the West Nile virus was identified in tissue specimens taken from both crows and a Chilean flamingo that had died at a zoo in the vicinity.

Within five years the virus had spread to all forty-eight contiguous states and several provinces in Canada. There were major flares of WNF and WNND in 2002 and 2003 with almost 3,000 cases of WNND in those years.

Then things calmed down and, as is typical, the money available for mosquito control became less abundant. The disease spread to Argentina by 2005 and eventually to most of the Western Hemisphere countries. Strangely only the United States (and Canada) suffered major epidemics.

And then came 2012.

Dallas County had a population of nearly two and a half million humans; of those 255 developed WNF, another 173 got WNND and 19 of those died. The review article, published in the July 17, 2013 edition of JAMA, states there was "An usually rapid and early escalation of human cases (which) followed infection trends in mosquitoes."

As in the rest of the country, Dallas had experienced a considerably warmer than usual winter. Ever since 1966, when aerial spraying for mosquitoes was instituted for an epidemic of St. Louis encephalitis, researchers in the metropolitan area had a heightened awareness of arthropod-bourne disease. Blood studies of residents in a Dallas area prone to flooding had shown there had been recurring epidemics of related virus-caused illness.

As West Nile virus supplanted its predecessor, Dallas began to experience cases of WNND and to prepare for its flares. In May 2012 a mosquito trap yielded evidence of West Nile-infected insects and all area physicians were sent a recommendation to test patents with symptoms of potential WNND for the virus.

A "vector index" was developed and calculated weekly; the specific of the math doesn't matter, but it related to how many of the particular mosquito species which was the region's primary carrier of West Nile virus, Culex quinquefasciatus, were found and their infection rate. Human cases of WNND were noted to follow the vector index peaks by one to four weeks.

One means of prevention: avoid being bitten

One means of prevention: avoid being bitten

An 8-day aerial spraying of insecticide did not lead to an increase in emergency room visits for asthma or other respiratory problems, or, for that matter, to skin rashes.

As of today I'm unaware of any human vaccine for West Nile or any treatment for the disease other than supportive measures.

So what can we do to prevent WNF or WNDD?

At present our only method is to control the mosquito population and avoid being bitten. I decided to change the drinking water we put out for the birds we feed and any dog water that's outside every other day. And we don't garden in the evening.

I'll mention one other, low-tech preventive measure in my next post.










Still too much salt for adults and for kids

Monday, March 25th, 2013

The American Medical Association newsletter for March 22, 2013, focused on our excess salt (sodium chloride) intake threatening the health of both adults and kids in this country. Two major studies were discussed.

Let's leave most of this salt sitting there.

Let's leave most of this salt sitting there.

The ABC Medical Unit blog on the subject had the title "1 in 10 U.S. deaths blamed on salt." The research came from a Harvard epidemiologist, Dr. Dariush Mozaffarian who links excess dietary sodium worldwide to almost 2.3 million deaths yearly (2010 data). The same researcher had a project looking at the impact of added-sugar beverages; now he concludes that excess sodium was a worse culprit.

The question has always been whether reducing dietary sodium intake, widely acknowledged to reduce blood pressure, can also positively impact the occurrence of cardiovascular disease. One classic article, published in the British Medical Journal in 2008, originally studied ~3,000 adults with prehypertension (i.e., blood pressures that aren't over the 140/90 limit, but are trending that way; Mayo Clinic staffers uses 120-139 over 80 to 89 to define the entity). The group, age 30 to 54, were enrolled for one to four years in randomized lifestyle intervention trials, called TOHP (trials of hypertension prevention). The long-term effects on the TOHP participants (over 10 to 15 years) showed  cardiovascular disease events (heart attacks or strokes) were less frequent (25-30%) in the group originally assigned to a lowered salt intake diet.

Many of us eat (or in my case used to eat) a diet higher in sodium than is currently recommended. I cut way down on salt nearly thirty years ago when my blood pressure crept up, eating out less often, not purchasing packaged foods unless their labels revealed relatively less salt, cooking with half to a third of the salt a recipe suggested and not adding salt at the table. There is evidence that our preference for eating salty foods can "reset" in about three months on a reduced salt diet and I would certainly concur with this; salty foods just taste bad if I try them now.

Dr. Mozaffarian's data, recently presented at an American Heart Association (AHA) meeting in New Orleans, was a compilation of 247 surveys on sodium intake and 107 clinical trials. The latter set examined both salt's effect on blood pressure and the logical, though unproven corollary that lowering BP can have a positive effect on the development of cardiovascular disease (CVD).

The results strongly support the evidence that high-salt packaged and processed foods contribute to our epidemic of CVD. Dr. Mozaffarian was quoted as saying bread and cheese are the top two sources of sodium in the U.S. diet.

Another of the researchers involved in the study was quoted as saying, "This study is the first time information about sodium intake by country, age and gender is available. We hope our findings will influence national governments to develop public health interventions to lower sodium."

That would be wonderful, but in the meantime, it's up to us (and I'll say this over and over) to read labels for sodium content.

As usual the Salt Institute tried to minimize the research's impact on the average American, saying it hadn't yet been published in a peer-reviewed journal and was misleading. Of course they make their living selling and promoting salt, so I take their comment with a grain of...pepper.

A second study, presented at the same AHA conclave, said that 75% of people around the world consume much more than the recommended amount of salt. Figures from 2010 said the worldwide average was close to 4,000 milligrams per day as opposed to the World health Organizations suggested 2,000 mg and the AHA's newer 1,500 mg figure.

The clues to having less salt in your diet: start with reading labels (we've done this for years, deliberately picking, for example, lower-salt versions of spaghetti sauce and cheeses. Obviously, as I've written before, avoiding pre-packaged meals in favor of fresh vegetables and fruits is another salt-avoidance technique. Re-training your palate, as noted above, may be easier than you think.

Not a great choice for this toddler's snack; try carrots instead

Not a great choice for this toddler's snack; try carrots instead

Another study, headed by Joyce Maalouf, a fellow at the CDC's National Center for Disease Control and Prevention, was featured online by Science Daily on March 21, 2013. This one looked at pre-packaged foods for young children in the United States. Over 1,100 products sold in our grocery stores and designed for the baby and toddler market were evaluated. A cutoff level of 210 mg of sodium per serving was established and toddler meals, on average, exceeded that level 75 percent of the time, some by a factor of three (630 mg of sodium per serving).

Let's look at the logic. If it only takes three months to educate an adult's sense of what's enough salt in a meal, then it seems to me we're training our toddlers to prefer high-salt food items when they are too young by far to be doing their own shopping.

The take for us as parents and grandparents is to read labels, not only on foods that we may choose for ourselves and the adult members of our families, but also (and especially) for our youngsters.

Maalouf's data, highlighted in a CNN article online mostly looked at pre-packed meals that are typically heated in a microwave. She noted that the USDA recommended total intake levels for toddler sodium consumption were 1,000 to 1,500 mg per day.

My experience with kids at the that age is like hers (while much more limited); they are "walking appetites" and in some households are allowed to eat six to eight snacks a day. That can add up to an enormous amount of salt and form dangerous eating habits that last a lifetime.

Again the basic lesson is the same: read labels and vote with your choices of lower-sodium foods. If enough of us quit purchasing high-salt items, they will eventually go off the market.

And ignore the voices of those whose basic interest isn't your health or that of your children, but rather their own profit margin.


Cholera: Part two, the nearby 21st century epidemic

Tuesday, February 26th, 2013

Until 2010 I hadn't thought much about cholera in the modern era. I had considered it a disease from the past  and associated it with Dr. John Snow, the father of modern

Algae can carry cholera bugs a long ways

epidemiology , the study of the patterns, causes and effects of health and disease in defined populations (Hippocrates, the famous Greek physician is considered the ancient father of the field).

I was clearly wrong in doing so.

I had previously read parts of the science writer Laurie Garrett's first two books, The Coming Plague: Newly Emerging Diseases in a World Out of Balance published in 1994 and Betrayal of Trust: the Collapse of Global Public Health which followed in 2000. Her first book touches on cholera in Africa and then has a section on the seventh Global Pandemic starting in 1961 in Indonesia's Celebes Islands.

Now I read Chapter 16 of The Coming Plague in detail. It mentioned that Rita Colwell, PhD, an  environmental microbiologist, was convinced in the 1970s and 1980s that bacteria and viruses could be carried in algae, the world's  oldest living life form. Algae are responsible for "red tides"  (AKA Harmful Algal Blooms or HABs), episodes when those ocean plants massively increase in number then produce toxins making shellfish dangerous to eat and killing off fish.

Colwell found that the bacterium responsible for cholera could survive encysted in algae and float long distances in their "plant capsules." The El Tor strain of the bug was responsible for the 1991 epidemic in Peru. The CDC's publication Morbidity and Mortality Weekly Report, AKA MMWR, mentioned that outbreak in its February 15, 1991 editionMMWR noted this was the first appearance of cholera in South America in the 20th century and recommended exclusive use of boiled water for drinking, careful cleaning of fruits and vegetables, and avoidance of raw or inadequately cooked fish or other seafood. It stated the risk to U.S. travelers was low.

In the next eleven months cholera claimed over 330,000 victims in the Western Hemisphere, killing just over 1%. Lima, the Peruvian capital, had stopped chlorinating its water and Peruvians often ate ceviche, uncooked fish and shellfish mixed with lime juice. By the Fall of 1993, 8,000 deaths and over 900,000 cases of cholera were reported in Latin America. The El Tor strain of the cholera bacterium had become endemic in the region.

A 1994 article in the Journal of Clinical Microbiology documented the next chapter in the modern history of cholera. A new strain struck in December of 1992, first in the Indian city of Madras and then spreading to Calcutta, Bangladesh and Thailand. Even those who had previously been through a siege of cholera were not immune to the O139 strain as the Bengal cholera Vibrio was termed.

An earthquake can be both a disaster in itself and the seed for an epidemic.

The Western Hemisphere would have another cholera epidemic eight years later. In the January 10, 2010 a major earthquake in Haiti occurred. Although its magnitude on the logarithmic Richter scale was "just" 7.0, while the offshore earthquake in Japan in 2011 was an 8.9 (an 8.0 quake is 10 times as intense as a 7.0 and a 9.0 is 100 times as powerful), the depth of the Haiti quake was ~half that of the 2011 tremor in Japan and it struck a major Haitian city. The damage was immense and the local infrastructure was severely disrupted with healthcare, water and sanitation being affected.

A recent New England Journal of Medicine article (Feb 14, 2013) reviewed the surveillance efforts during the subsequent two years. Prior to the earthquake, less than two thirds of Haiti's population of 9.8 million had access to even the lowest category of an improved water source; less than an eighth drank treated water from a pipe system and only a sixth lived with adequate sanitation. The 1991 Peruvian cholera didn't reach Haiti so there was little or no prior immunity to the El Tor Vibrio strain.

The results were predictable, a major outbreak of cholera, but the government and international medical assistance markedly ameliorated the epidemic. Through October 20, 2012 over 600,000 cases of cholera were reported and 7,436 deaths resulted. The case fatality rate was initially high in some locales (4.6%), but within three months of the start of the epidemic it fall to the World Health Organizations target of <1.0%.

In comparison there were 2.8 million cases of cholera globally in 2011 with 91,000 deaths (3.25%). The CDC notes that twenty-three cases occurred in the U.S.; 22 were associated with travel to Haiti, one with consumption of food products from that country.

The treatment of cholera is relatively simple: the WHO says rehydration with oral rehydration salts is enough in almost all cases. Intravenous administration of fluids can be life-saving in especially serious cases.

But how about preventing the disease?  A Perspective column in the same journal edition (NEJM Feb 13, 2013) is titled "The Cure for Cholera--Improving Access to Safe Water and Sanitation." The three authors, all with dual MD, MPH degrees, note that the malady is still a major source of illness and mortality in the developing world with WHO estimating 3 to 5 million cases and 100,000 to 200,000 deaths a year.

In the treatment arena, they note that antibiotics should be given to those with even moderate dehydration, that all patients should receive zinc, which can decrease the duration of diarrhea, and a newer variant of the two-dose vaccine should get wider usage.

Safe drinking water and modern sewage disposal is still a major issue for many in 2013: two and a half billion live without adequate toilet facilities and nearly 40% in the least developed regions of the world don't have bacteria-free water to drink.

More than a billion of the poor and marginalized need help. But estimates of $50 billion needed per year are daunting in these tough economic times.



Cholera: Part 1 background and history

Sunday, February 24th, 2013

An 1882 monument to victims of cholera

Cholera is an infectious illness, found only in humans, caused by a bacteria in contaminated water, leading to severe diarrhea and dehydration and capable of killing its victims in a matter of hours if untreated. When I read about the disease for the second time in decades (the first time was after a 21st-century epidemic in Haiti), I was amazed at how quickly a victim can lose 10% or more of their body weight in severe cases; e.g., eight quarts between my normal bedtime and when I usually wake up. Many people who ingest the bacteria don't develop any symptoms, but if they do and lack modern re-hydration therapy, their chance of dying is 40-60%.

In all likelihood it is an ancient disease with writings from the lifespan of Buddha  (563-583 BCE) and from the time of Hippocrates (460-377 BCE) revealing diseases that presumably were  cholera. It has, over the last several hundred years, been a major killer of mankind, causing millions of deaths in the 19th century.   Those numbers place it among the deadliest of infectious illnesses, in the company of smallpox, the Spanish flu, bubonic plague, AIDS and malaria.

A CBC News article online with the title "Cholera's Seven Pandemics," starts with a major outbreak in India near the Ganges River delta. Between 1817 and 1823 there were 10,000 deaths among the British soldiers stationed in that country, estimates of hundreds of thousands of fatal cases among native Indians and 100,000 dying in Java in the year 1820. The second pandemic began in 1829, again in India, and spread to Russia, Finland, Poland, England, Ireland, Canada, the U.S. and Latin America, before another outbreak in England and Wales that killed 52,000 over two years. The sixth pandemic killed more than 800,000 people in India alone and, over the next 24 years swept over parts of Europe, Russia, northern Africa and the Middle East.

The National Library of Medicine's website entry on cholera associates it with crowding, poor sanitation, famine and war. India has remained a source as the disease is endemic (ever present) there. People get cholera by eating or drinking either contaminated food or water; the medical term is the fecal-oral route.

In the summer of 1854 London was the epicenter of a deadly outbreak. Dr. John Snow, a famous British physician born March 15th, 1813, had been noted as a pioneer in anesthesiology, using chloroform to assist in Queen Victoria's delivery of her eighth child in 1853.

Then, as documented in the book, The Ghost Map by Steven Johnson, Snow turned his investigative talents and keen mind to cholera, becoming in the process the modern father of epidemiology.

London's population had grown immensely and its sewage system was antiquated. In addition to basements filled with excrement, cesspools and drainage into water sources were rampant. A major concept of disease causation was the miasma theory. The term means "bad air" and the assumption was illness was caused by the presence in the air of a miasma, a ill-smelling vapour containing suspended particles of decaying matter .

Snow, on the other hand, felt cholera was caused by something ingested, most likely by drinking water contaminated by waste products.

In a painstaking and extremely clever investigation, Snow had, in a prior cholera outbreak in 1849 which was responsible for a dozen deaths in flats in a slum area, shown that two separate  sets of milieu had markedly differing death rates. All environmental parameters were essentially identical in the two groups with one exception; where they obtained their water. The group who suffered a much higher rate of illness got theirs from a company whose river source was in the same area where many sewers emptied.

Vibrio cholerae, the cholera bacteria

Five years later a much larger cholera epidemic provided an opportunity to more closely examine the water sources of the victims. One particular pump, seemingly providing clear water, proved to be the culprit. The Broad Street pump's output was examined by a Snow's colleague, a skilled microscopist Dr. Arthur Hassall, and found to contain what Hassall believed to be decomposed organic matter with oval-shaped tiny life-forms felt to be feeding on that organic substance. Snow was not aware then of the 1854 work of an Italian scientist, Filippo Pacini, who had examined the intestines of patients dying from cholera in Florence and found a comma-shaped bacillus he termed a Vibrio.

The proponents of the miasma theory did not yield easily, but Snow's map of the location of deaths from cholera eventually let his hypothesis of a water-borne illness prevail.  Then an assistant curate (church figure in charge of a parish) named Henry Whitehead who had read Snow's papers on the epidemic eventually found the index (first) case, a baby Lewis. As a result, the Broad Street pump was excavated and a direct connection to a cesspool was found.

The juxtaposition of Snow's scientific data and Whitehead's work as a beloved neighborhood figure led to the local Vestry Committee's report endorsing the water-as-culprit theory.

The city subsequently launched a major project to carry waste and surface water away from Central London.





Five years later, he