Q. Is it true that there are worms in fish that can cause infections in humans?

A. Yes. Two types of infections are possible from eating raw fish harboring the larvae of worms. One, anisakiasis, is caused by the larval stage of several types of roundworm found in both the organs and flesh of marine fish. The condition appears most often in the Netherlands and Japan, where the practice of eating raw fish is common.

In the syndrome as it occurs in those countries, the larvae penetrate the lining of the stomach and intestine and attach themselves beneath the surface. Symptoms include both abdominal problems and fever and may resemble appendicitis and intestinal obstruction. Fewer than 20 cases of anisakiasis have been documented in North America, including six in California, five in Alaska, and four on the North Atlantic coast. In all of them, symptoms were mild.

But the worms are commonly found in fish caught in North American waters, and most authorities believe that many more cases go unreported. The infection is entirely preventable by avoiding raw or poorly cooked fish. Larvae are killed at 140 degrees Fahrenheit, or by freezing at temperatures below zero degrees Fahrenheit for several days.

The second type of infection is attributed to fish tapeworm. It occurs after ingesting the larvae of a species called diphyllobothrium, found in the flesh, liver and roe of fresh-water fish such as pike and perch, as well as in anadromous fish like salmon which swim from the sea to a river to spawn. The organism has a marked affinity for vitamin B-12, and in some infected individuals depletion of B-12 produces an anemia resembling that of pernicious anemia. Other frequent symptoms include fatigue, diarrhea, dizziness, weakness, numbness of the extremities and a feeling of hunger.

Again, the incidence of infection in the United States is unknown. However, between 1978 and 1981 the Centers for Disease Control received between 133 and 272 requests per year for a drug used to treat the condition. As with anisakiasis, it is thought that most cases went unreported.

Fish tapeworm is also completely preventable by thorough cooking of the fish or freezing it at zero degrees Fahrenheit for 24 hours.

Q. We live in a community where the water supply is not fluoridated, so I give my baby fluoride drops. The pediatrician recommended that I give them between feedings. Why? Also, is there any benefit to giving fluoride drops separately from a vitamin supplement, rather than in a preparation together with a multivitamin?

A. It is a good idea to give fluoride drops between feedings to ensure maximum absorption of the mineral. When given on an empty stomach, it is completely available. If taken with milk or with a meal containing considerable calcium, absorption will be hindered.

The problem is that it is more difficult to remember to use the drops apart from feedings. It helps if you can associate it with some between-feeding, fairly routine part of the daily schedule, possibly before the baby's morning nap, or perhaps just after waking up from the afternoon nap. In older children it is suggested that fluoride be used immediately before bedtime, after the teeth have been cleaned.

To answer your second question, there is no evidence of any advantage in taking fluoride separately from a multivitamin preparation. What is important is that your child take the appropriate dosage for his age. For that information, you must check with your pediatrician.

Q. Recently I ate a passion fruit for the first time. It was expensive, but I rationalized that it was a better buy than a rich dessert with calories I didn't need. Can you tell me how many calories a whole fruit contains and whether it provides any nutrients?

A. A one-ounce piece of fruit has just 18 calories, which makes it a particularly good choice for anyone who is counting calories. It also provides some vitamin C as well as small amounts of vitamin A and B vitamins. The passion fruit is also called a purple granadilla (from a Spanish word meaning little pomegranate). There is a yellow as well as a purple variety. As you might expect, passion fruit comes from the same group of plants as the well-known passion flower, which is associated with the Signs of Passion.

According to "Jane Grigson's Fruit Book" (Atheneum, 1982), the flower, which is native to Brazil, was especially prized by Spanish Jesuit missionaries who believed that it had been thoughtfully arranged by the Creator and planted in the New World to help in the conversion of the Indians. Indeed, most of the species are grown for their ornamental flowers rather than for the fruit. The flowers of the fruit-bearing varieties are not especially impressive.